07:17 Good morning and welcome to the first morning of Formula 1 pre-season testing for 2015 from Jerez in Spain.

AUTOSPORT Live will be bringing you as-it-happens coverage and analysis from all three winter F1 tests, starting from today to Wednesday at Jerez and followed by two further sessions at Barcelona from February 19-22 and February 26-March 1.

07:29 Here's who is scheduled to drive on the first day of the test. Obviously, this is dependent on each of the cars being ready to run.

Mercedes – Nico Rosberg
Red Bull – Daniel Ricciardo
Williams – Valtteri Bottas
Ferrari – Sebastian Vettel
McLaren – Fernando Alonso
Toro Rosso – Carlos Sainz Jr
Lotus – Pastor Maldonado
Sauber – Marcus Ericsson

07:32 The fastest time from the opening day of testing here in 2014 was a 1m27.104s, set by Kimi Raikkonen. It will be interesting to see how much quicker the pace is today after what was a very stuttering start last year.

07:32 There's half an hour until the track opens here in Spain. It's clear and sunny (although the sun is still very low!), and the air temperature is a chilly 3.4C. Track temp is even lower at 2.8C.

07:38 EDD STRAW: "Last year, the opening morning of the test was extraordinary, with the pitlane still full of people from the early-morning rollouts even when the track was open.

"Only 93 laps, many of them stuttering, were run that day and the idea that the cars would be ready to contest a grand prix a month-and-a-half later seemed ridiculous. It's testament to the effectiveness of even the smaller teams that everyone was ready for the Australian GP."

07:39 The new Lotus E23 is a bit behind schedule for the first test. Parts are still on their way to the circuit and the car is not likely to appear until after the test is well under way.

07:43 AUTOSPORT has a four-person team here at Jerez: Jonathan Noble, Ben Anderson, Glenn Freeman and Edd Straw.

07:58 Just a couple more minutes before the circuit opens - we've sent JONATHAN NOBLE and EDD STRAW down to the pits to keep an eye on what's going on.

One of the main things they'll be looking out for is a first glimpse of the Red Bull RB11 - the only car we've not seen anything of (in real or 'rendered' form) so far.

08:00 It was basically still dark at Jerez when Mercedes took the covers off of its F1 W06 in the pitlane around 40 minutes ago, but the sun is now creeping up from behind Turn 5.

08:01 Rosberg, Vettel, Ricciardo and Ericsson are the first to fire up their engines and head for the pit exit. Testing is under way at Jerez.

08:04 EDD STRAW captures the first overtake of the year.

Rosberg gets to the end of the pitlane first but Vettel drives past him while the Merc is parked and preparing to launch.

08:05 All four back in the pits after installation laps. Quiet descends on the Jerez pit.

08:05 Meanwhile, here's the news behind world champion team Mercedes launching its new cars this morning. Williams has also pulled the covers off its 2015 challenger.

Mercedes launches as testing begins

New Williams makes first appearance

08:07 JONATHAN NOBLE: "When the Red Bull returned to the garage the team were keeping it closely under wraps - hiding it behind screens as soon as it pulled up.

"Toro Rosso driver Max Verstappen is currently down here outside the Red Bull garage taking a look at the RB11 too."

08:08 BEN ANDERSON: "There will be much interest in Fernando Alonso's debut with McLaren-Honda today.

"Honda's first V6 turbo hybrid engine suffered a troubled first test in Abu Dhabi in November, as the team chased a persistent electrical problem, so it will be interesting to see if they've made progress.

"McLaren says it is still working on the MP4-30 so won't take to the track immediately."

08:08 EDD STRAW: "The Merc is back in the garage and the doors have come down. It was smoking a little when it left the pits, and Rosberg seemed to struggle to get away."

08:11 For those of you just joining us (it's OK, we know it's a Sunday), we've had installation laps from Rosberg (Mercedes), Vettel (Ferrari), Ricciardo (Red Bull), and Ericsson (Sauber).

08:12 JONATHAN NOBLE with more on the closed Mercedes garage:

"Grinding noises coming from Mercedes - they must be cutting some bodywork."

08:13 And EDD STRAW adds that similar noises can be heard coming from the Red Bull garage as well.

08:15 EDD STRAW: "Doors are opening at Toro Rosso - with the inevitable screens being re-arranged to ensure nobody sees in"

Thank goodness teams are banned from using those screens on GP weekends these days.

08:16 Here's a look at that camouflaged Red Bull design heading out of the pitlane.

08:16 @McLarenF1: "Fire-up successfully achieved. Systems checks now in progress."

08:17 Carlos Sainz Jr is putting his helmet on, so it looks like the Toro Rosso isn't far from being ready to take its first lap.

08:17 BEN ANDERSON: "Nearly all teams have talked about 'tighter packaging' when revealing their new cars.

"Better aerodynamics is always the name of the game in F1, but given how critical cooling was with the new V6 engines last year some caution is clearly required.

"Grinding noises coming from the Mercedes and Red Bull garages suggests maybe old habits die hard..."

08:17 EDD STRAW: "There's some blow-drying work going on outside Red Bull's garage to clear up patches of water in the pit box area."

08:19 Just to confirm - that's not water from a leaking car that's being dried in the Red Bull pit. Just damp patches that haven't dried from overnight as the pits are still in shade.

08:20 EDD STRAW spots new Ferrari tester Esteban Gutierrez getting used to his new surroundings (and jacket) in the pitlane.

08:21 Toro Rosso is putting the wheels on the car, and Jos Verstappen has joined son Max in the garage to watch the car head out shortly.

08:22 EDD STRAW: "I could hear the Williams engine turning over in their garage at the pit entry-end of the pits, but it's been turned off now."

08:23 Sauber tweets that Ericsson will be back out for a second lap soon.

08:25 Sure enough - the Sauber heads back out as promised.

08:26 A correction from EDD STRAW regarding his earlier Williams fire-up comment - that was in fact the Sauber garage that was making all that noise a few minutes ago.

08:26 McLaren tweets pictures of some rather special preparations taking place on its new car, as Fernando Alonso's #14 is added to the livery:

"Applying the finishing touches"

08:27 Ericsson is the first driver to stay out for a second lap - will he stay out to be the first to set a time as well? If he does, it won't be anything special, as he's just backed off heading into Turn 4.

08:28 Sainz heads out for his first lap as a Toro Rosso race driver.

08:29 EDD STRAW reports that the Sauber was stuttering coming out of the final corner last time around - and that Sainz's departure from the garage was met with applause from the Spanish crowd.

No laptime from Ericsson - he returns to the pits.

08:30 Sainz heads back to the pits having completed an installation lap in the new STR10. All quiet on-track once more.

08:32 Fernando Alonso has just walked into the back of the McLaren garage. JONATHAN NOBLE spotted a notebook in his hand - it didn't exactly look like the Spaniard was about to suit up and hop in the MP4-30 just yet.

08:33 EDD STRAW: "All quiet at Red Bull - garage shutters down at the moment."

08:36 JONATHAN NOBLE: "Good to see the Spanish crowd out in force at Jerez today. Earlier on Mercedes fired up its W06 in the garage - possibly to check on any bodywork heating - a few minutes after some grinding noises were heard from the garage. When it didn't go out, there was a lot of applause and cheering from the grandstand opposite the pits."

08:36 The Red Bull heads back out on track, defying EDD STRAW in the process.

08:37 More from our man on Red Bull watch - he reports "lots of popping and banging" from the Renault-powered RB11.

08:38 Ricciardo stays out - will he be the first driver to complete a flying lap in 2015?

08:39 He is - a 1m29.141s for the Red Bull.

08:39 While down on Red Bull watch, EDD STRAW grabbed this shot of the team marking out its pit area.

08:41 Ricciardo pits, so that was a straightforward three-lap run for the Red Bull.

08:43 JONATHAN NOBLE: "As well as a fantastic livery, Red Bull can already breathe easy that 2015 testing is going better than last year.

"Twelve months ago on day one, Sebastian Vettel managed just three installation laps without setting a time on the first day of running.

"Daniel Ricciardo has a four lap tally already and has even completed a flying lap - the only man to do so so far."

08:43 Rosberg heads back out in the Mercedes. The grinding of the W06 is over for now...

08:44 EDD STRAW: "At the start of Ricciardo's second lap, the rear end of the car was bottoming out and sparking on the run up the hill into Turn 1.

"When the car returned to the pits there was a clear smell of burning - although that's not unusual for a new car."

08:44 You can have a browse through all the 2015 Formula 1 designs we've seen so far in our gallery from the launches and unveilings:

2015 Formula 1 car launches

And as the test develops, we'll be uploading hundreds more hgh-res action shots into our gallery section so you can have a thorough look at the field.

08:45 Rosberg stays out for a second lap.

08:45 Red Bull wasted no time in getting the 'fan (un)friendly' screens up over its garage as Ricciardo came back in, though EDD STRAW did his best to sneak a phone camera through.

08:46 The Mercedes is 1.8s slower than the Red Bull's benchmark through the first sector, for those who are interested in the meaningless times of pre-season day one.

08:47 Rosberg completes his first flying lap - he slots into second with a 1m30.841s. That's 1.7s slower than Ricciardo's first lap.

08:47 Mercedes chief Paddy Lowe briefly headed over to the pitwall for a look at the F1 W06 flying past, but he's made his way back to the garage.

08:48 Rosberg stays out and goes much quicker this time - a 1m26.933s puts him 2.2s ahead of Ricciardo.

08:48 It's still very cold here in Jerez. Air temperature a little over 5C now, while the track temperature has yet to top 10C.

08:48 Vettel heads back out in the Ferrari.

08:49 Rosberg shaves (or chops) nearly two seconds off his best that time around - he's down to a 1m25.057s in the Mercedes.

08:51 Rosberg finds more than a second on his latest lap - a 1m23.986s is the new benchmark as the Mercedes continues to pound round on this run.

08:52 Vettel sets his first laptime as a Ferrari driver - a leisurely 1m35.218s.

08:52 Rosberg finds another three tenths to get down to a 1m23.6s.

08:53 Ericsson heads back out in the new Sauber C34, so we have three cars on circuit simultaneously now.

08:53 Vettel picks up the pace in the Ferrari - a 1m29.252s has him just behind Ricciardo now.

08:55 Rosberg is back in the pits after that flurry of fastest times on his first proper run.

EDD STRAW: "Mercedes is starting 2015 the same way it started 2014 - by running further, earlier, than anyone else.

"Whenever the car returns to the pits, the mechanics are quick to cover the upper parts of the rear wing from prying eyes."

08:56 Vettel finds a chunk of time to go second fastest in the Ferrari. Almost within two seconds of the Mercedes now.

08:56 Ericsson posts his first flying lap of the test in the Sauber. The Swede is third fastest, fractionally quicker than Ricciardo's Red Bull.

08:57 He's a couple of seconds faster next time through, which puts him in a no-man's-land between Vettel's Ferrari and the RB10.

08:58 We have our first red flag of 2015 testing.

08:59 Ericsson is the only car on track, although it seems that he's still running.

08:59 The Sauber took more than a minute to get through the short first sector, so maybe he stopped and then got going again. He's back in the pits now, anyway.

09:00 Sure enough - the track is green again. A temporary blip for the Sauber.

09:01 Some commotion outside the McLaren garage just now. Looks as though the first run of the MP4-30 is getting closer.

09:03 EDD STRAW reports that as Carlos Sainz Sr appears in the Toro Rosso garage, his son is getting ready for another run. The team has just been blipping the engine in the garage in preparation.

09:05 First hour summary:

* Red Bull causes a stir as its 2015 car emerges in camouflage colours

* Mercedes and Williams officially launch their new designs

* Rosberg sets early pace for Mercedes

* Ericsson causes a brief red flag

* Mercedes, Red Bull, Ferrari, Sauber and Toro Rosso all run, but McLaren, Williams and Lotus yet to appear

09:06 Ricciardo heads back out in the camo-liveried Red Bull, while the McLaren-Honda has just fired up in the garage.

09:10 Ricciardo abandons that flying lap and heads back to the pits, just as Rosberg heads back out in the Mercedes. The German stopped at the end of the pitlane and pulled away very gently. All quiet again in the McLaren garage...

09:12 Sainz heads back out in the Toro Rosso for his second lap of the day.

09:13 Rosberg continues to make strides in the Mercedes. The first flying lap of this latest run is faster still - 1m23.325s is the new benchmark on day one.

09:15 EDD STRAW was down at the pit exit as Rosberg set off. He reports that the Mercedes stopped briefly but didn't do a full-fledged practice start.

09:15 Rosberg improves again on his next lap. He's beaten the best time of the entire four-day Jerez test last year (Kevin Magnussen's 1m23.276s) by 0.170s in just 11 laps... Meanwhile Sainz is now off the mark - third fastest on a 1m26.081s.

09:17 Rosberg has settled in with a couple of mid-1m23s in succession on this run, slightly slower than his 1m23.1s that currently tops the times by 2.6s from Vettel.

09:18 Sainz pits in the Toro Rosso, having taken his lap count up to five so far today.

09:20 Rosberg has the track to himself at the moment, and he's still comfortably lapping in the 1m23s on this run.

09:21 Vettel makes it two cars on track, taking the Ferrari back out to join the Mercedes.

09:24 Rosberg is on his 10th flying lap of this run on a set of medium-compound Pirellis, and his pace isn't falling off very much at all so far.

09:26 Three cars on track now - Ricciardo joins Rosberg and Vettel.

09:27 Rosberg comes in to complete a run of 10 timed laps - Vettel follows him down the pitlane.

09:27 The first red flag of the year only lasted a few seconds and was caused by Marcus Ericsson's Sauber doing this and then getting going again. He made it back to the pits unscathed.

09:28 The crowd outside the McLaren garage continues to swell as the Honda engine is fired up again.

09:28 Ricciardo moves up to second with a 1m25.703s.

09:29 Rosberg's 10-lap run on medium compound Pirelli tyres looked pretty impressive, though we don't have much to compare it with yet. He lapped consistently in the mid-to-late 1m23s for the majority of the run, after setting that new fastest time of the test early on.

09:29 Another improvement for the Red Bull, this time Ricciardo gets down to a 1m25.131s. He's two seconds adrift of Rosberg.

09:30 Ricciardo is on the hard tyre, while Rosberg's best lap was set on mediums.

09:31 Ericsson heads back out in the Sauber to make it two cars on track.

09:34 Ricciardo didn't stay out for long, while Ericsson comes through to set a 1m28.6s.

09:36 Ericsson improves to a 1m26.589s, but the Sauber is still fifth out of the five cars to have set a time. Sainz heads out to join him on track, to the excitement of the growing Spanish crowd.

09:37 EDD STRAW reports from the pits that Sainz carried out a practice start to kick off this run.

09:38 The revving Toro Rosso at the end of the pits certainly caused some excitement in the media centre - presumably from people who thought it was the McLaren-Honda, which is sat directly underneath us in its garage at the moment.

09:38 Ericsson moves above Sainz for fourth with a 1m26.080s.

09:40 The Sauber deposes Vettel for third now as Ericsson moves into the 1m25s.

09:42 We have our first sighting of the McLaren-Honda. Alonso has left the pits.

09:43 Alonso coasts through the first sector, heading out of our sight as he swoops right through Turn 5 and onto the backstraight.

09:45 The McLaren is back in the pits. EDD STRAW reports that it looked and sounded "very stuttery" both in the pits and out on track as Alonso logged that first installation lap of the test.

09:50 Rosberg - already with a 10-lap run under his belt this morning - heads back out, and Ricciardo joins him in a Red Bull that does not sound happy on its pit limiter at all.

09:53 BEN ANDERSON reports from the pits that cooling is the order of the day at Toro Rosso now Sainz is back in the garage. "Fans are on full blast," he says.

09:53 Rosberg and Ricciardo are both lapping in the mid-1m25s at the moment.

09:55 Ricciardo dips into the 1m24s for the first time today, closing the gap on the Mercedes to 1.5s.

09:57 BEN ANDERSON has spotted a "relaxed-looking" Ron Dennis wandering up the pitlane from the McLaren garage following that first lap for the Honda-powered MP4-30.

09:58 As a rough indication of how much progress has been made with these new generation of F1 cars and power units, Nico Rosberg's fastest time this morning is four seconds faster than the quickest overall on day one at Jerez last year.

09:59 Here's a lap count after nearly two hours of running:

Rosberg (Mercedes) 26
Ricciardo (Red Bull) 16
Ericsson (Sauber) 15
Sainz (Toro Rosso) 14
Vettel (Ferrari) 9
Alonso (McLaren) 1

No sign of the Williams or the Lotus yet today, although the former was at least rolled out into the pits for some photographs first thing.

10:01 BEN ANDERSON: "It's amazing how smooth the Mercedes engine note sounds one year on from the debut of the V6 turbos. They sounded so rough and unrefined this time last year."

10:04 As Ericsson takes the Sauber out to join Rosberg (doing high 1m25s) and Ricciardo (who has now dropped into the 1m26s and is less consistent), BEN ANDERSON has taken a wander up to the Williams garage:

"Nothing much to see at Williams - screens are up and garage doors remain closed."

10:05 Ricciardo gets back into the 1m25s as Rosberg pits in the Mercedes.

10:08 Ericsson improves to a 1m24.804s in the Sauber, while Ricciardo is back in the pits with 22 laps to his name for the day.

10:10 Alonso re-appears in the McLaren for a second lap.

10:13 The McLaren is back in the pits for more checks, and BEN ANDERSON has an update from Williams:

"Just been chatting to Valtteri Bottas on the pitwall. Williams was delayed by some new car double checks yesterday. The team hopes to be out in around 15 minutes."

10:15 Now that the McLaren has twice made it back to the pits under its own (Honda) power, BEN ANDERSON notes that it marks a step forward from that troublesome debut test in Abu Dhabi at the end of last year.

10:16 Rookie Sainz rejoins with another practice start. Toro Rosso stressed yesterday that getting its young driver line-up familiar with the requirements of F1 is just as important as working on car development during these pre-season tests.

10:17 Bottas has told BEN ANDERSON that he expected all of the noses to look like the Williams solution this year, but his eye suggests that only Red Bull has gone down that route.

The Finn is pleased to see some variety on the grid, and with that he heads into the garage as the doors open and Williams appears to be preparing to head out for the first time.

10:21 Plenty more practice starts for Sainz, who is passing through the pits every time during this 'run'.

10:24 That short run is over for Sainz, who seemed to be making his getaways smoother with each attempt from the end of the pitlane.

10:28 Headlines from today so far:

* Rosberg sets commanding early pace in new Mercedes

* Alonso has his first lap in the McLaren-Honda

* Vettel completes his first proper laps as a Ferrari driver

* No movement from Williams and Lotus yet

* A quick spin by Ericsson causes only red flag so far

10:28 Outlap number three for Alonso in the McLaren-Honda breaks the silence at Jerez.

10:30 BEN ANDERSON: "The Honda engine note sounds cleaner than it did in Abu Dhabi but it's still unrefined. It sounds a bit deeper and throatier than the others at present."

And with that, Alonso returns to the pits again.

10:33 More from BEN ANDERSON on what McLaren is up to:

"The car is back in the garage and the screens are up following another single-lap run. This looks like the run plan McLaren racing director Eric Boullier wanted to get through in Abu Dhabi.

"If things go well expect some three lap runs from the McLaren later."

10:36 The track temperature is up to 16C now. No cars out on track. Currently fastest is Rosberg, 1.535s faster than Ricciardo's Red Bull. The Mercedes has also done the most laps, 31.

10:38 Alonso heads back out in the McLaren-Honda.

10:39 Alonso stays out for a second lap for the first time today, as some McLaren personnel head for the pitwall to catch a glimpse of the car going past.

10:42 Alonso posts a 1m40.738s as his first timed lap of 2015. That's 17s off the pace of Rosberg, but McLaren and Honda are working to a very different job list here in Spain.

10:43 Don't expect to see a Lotus any time soon:

@Lotus_F1Team: "E23 is in the air on its way to Jerez after firing up in Enstone yesterday, arrival expected later today."

10:43 Alonso is back in the pits, so as predicted by BEN ANDERSON that was indeed a three-lap run for the McLaren-Honda.

10:44 Bottas takes the Williams out for its first lap of pre-season testing.

10:45 Rosberg rejoins the action, stopping for a practice start before hand. The German sat at the end of the pits revving the engine several times before setting off.

10:46 BEN ANDERSON reports from the pits that Rosberg suffered "a lot of wheelspin" on that practice start attempt.

10:47 More McLaren-Honda observations from BEN ANDERSON in the pits:

"It sounds as though the McLaren is running limited power - the engine note has a strange stutter on full throttle at the end of the straight."

10:48 Williams kicks its 2015 test programme off with a single installation lap for Bottas - he's back in the pits.

10:52 Rosberg has the track to himself for what is shaping up to be a second long run of the day already. He's kicked this stint off in the 1m24s, and has just slipped to a 1m25.0s.

10:57 One of the fun parts of this early stage of pre-season is hearing what teams make of their rivals' cars. One team has speculated to BEN ANDERSON that Red Bull might not be running many 2015 parts today - aside from what is clearly a different nose to the RB10.

10:58 Still Rosberg rumbles round on his own out there. He's lapping in the mid 1m25s as Mercedes picks up where it left off in 2014 and gets down to some proper work before everyone else.

11:01 Ericsson and Sainz head out, giving us a rare moment (so far) with three cars on track.

11:04 With the new Lotus still on its way to Jerez, Williams starting late and McLaren getting to grips with the new Honda engine, it's been left to just five teams to do the bulk of the running so far. Here's the lap count just after midday at Jerez:

Rosberg (Mercedes) 43
Ericsson (Sauber) 24
Ricciardo (Red Bull) 22
Sainz (Toro Rosso) 19
Vettel (Ferrari) 9
Alonso (McLaren) 6
Bottas (Williams) 1

11:05 Ericsson was very lairy through the Turn 4 left-hander on that lap, the rear of his Sauber moving around significantly.

11:06 BEN ANDERSON: "I've just been chatting to Paddy Lowe of Mercedes. All seems to be going smoothly there.

"He also says that the busy grandstands here at Jerez are a good indication that Formula 1 is not in the crisis that some people say it is."

11:09 Rosberg and Ericsson are busy at the moment, both lapping in the 1m26s. It's fair to speculate that they are probably running different fuel loads, wouldn't you say?

11:12 Ericsson pits, so Rosberg is alone on track again as he clocks up his 50th lap of the day in the Mercedes.

11:14 @WilliamsRacing: "Valtteri remains in the car as we get ready for some more laps."

11:16 BEN ANDERSON can hear power tools being put to work behind closed doors in the Red Bull garage.

11:18 Whatever Alonso has spotted in the McLaren garage is amusing Jenson Button, Jonathan Neale and Eric Boullier greatly.

11:18 Niki Lauda joins fellow Mercedes chief Toto Wolff on the pitwall, and he waves in response to cheers from the crowd in the grandstands opposite the pits.

11:25 With Rosberg continuing to charge around - still in the 1m26s - Ericsson rejoins the action.

11:28 BEN ANDERSON: "Toto Wolff is hobbling around on crutches due to a bad knee. I can't remember the last time I saw him at an F1 event without an injury of some kind!"

11:28 Bottas heads back out for a second lap in the Williams.

11:29 Rosberg is back in the pits now, with 60 laps already chalked up for the Mercedes today.

11:29 Bottas stays out, so we could be on course to see a first timed lap from the Williams FW37.

11:31 Bottas opens his account with a 1m28.479s in the Williams, which slots him into sixth place between Sainz and Alonso.

11:32 Throughout the pre-season build-up, our technical writer CRAIG SCARBOROUGH will be analysing the latest designs and upgrades.

You can read his thoughts on the Mercedes W06 and Red Bull RB11 later today and tomorrow, but in the meantime, he's already provided the low-down on the McLaren MP4-30 and Ferrari SF15-T.

McLaren technical analysis - Clear signs of change

Ferrari technical analysis - A first recovery step

11:34 Bottas returns to the pits after that single timed effort.

The Williams is up to four laps for the day, two behind the McLaren.

11:35 Sauber is happy so far, declaring on Twitter that its 30 laps have been "encouraging".

11:37 Nothing on track at the moment, but the McLaren-Honda is being given another rev in the garage beneath our media centre at the moment.

11:40 There's no official lunchbreak during testing at Jerez, but we've seen in previous years that a lot of the teams tend to stop for a break around the same time. Things are pretty quiet at the moment, so that could be what's going on right now.

11:41 A slightly mournful tweet from a man who was here this time last year, Max Chilton:

"I have woken up feeling like something is missing, it's a F1 car in motion with the crisp morning air rushing under my visor. #stillhoping"

Stay chipper Max, you may well have a Carlin IndyCar to play with soon.

11:43 With the exception of Mercedes, which has clearly already got down to some serious work with Rosberg clocking 60 laps so far, the majority of teams will have pretty conservative goals for this first test, and particularly the opening day.

Toro Rosso technical director James Key explained last night what his team's first aim would be this morning: "Making sure it doesn’t catch fire, because when you look under the bodywork it’s incredibly tight!

"We will learn a lot about the tyres as well. And the drivers, we’ve got to get them ready for Melbourne so it’s normal. There will be a learning process for them but we want to get them as used to the environment that they are going to face as possible."

11:52 Our high-res Formula 1 2015 galleries are rapidly getting larger, so head this way to check out the new season's machinery in detail:

2015 F1 car launch gallery

Jerez F1 test gallery

11:54 We said it was probably lunchtime down in the paddock. Judging by this picture on Twitter, Rosberg is obviously so happy with the Mercedes F1 W06 that he doesn't want to leave it even for food!

11:56 Lunch dealt with - Rosberg is the first to return to the track. Bottas follows shortly after.

11:58 BEN ANDERSON: "Interesting to spend some time in the pits and see the new cars close up.

"The much-anticipated McLaren-Honda took a while to appear, but the renewed partnership has already completed more mileage than it managed in two days in Abu Dhabi last November.

"The engine sounds as though it is running limited power while Fernando Alonso and the team works through their test programme. The car seems to max out its speed halfway down the main straight and the engine note has a strange, wavy stutter to it."

12:00 BEN ANDERSON: "It's a bit ominous for the rest to see the Mercedes piling on the laps while others are in and out of the garage.

"The W06 sounds like its running very smoothly and technical chief Paddy Lowe, motorsport boss Toto Wolff, and non-executive chairman Niki Lauda cut relaxed figures on the pitwall.

"Red Bull is a massive 1.5s adrift on raw pace and Daniel Ricciardo hasn't managed any notably long runs - although 22 laps represents a giant leap compared to this time last year...

"I regularly heard the sound of cutting tools behind the closed door of the garage, so perhaps some of the packaging around Renault's updated engine is causing some problems. The engine doesn't sound nearly as refined as the Merc yet.

"By contrast, the Ferrari engine sounds a lot cleaner than it did last year and Sauber's Marcus Ericsson has racked up decent mileage in the interim C34. Not so much for Sebastian Vettel, as the Scuderia has spent most of the morning in the garage.

"So has Williams in actual fact. Valtteri Bottas told me the team planned to head straight out in the morning, but were delayed buy having to perform extra preparatory checks on the FW37.

"The car is at least up and running now."

12:01 Bottas improves his best time of the day, moving above Sainz with a 1m25.8s, and leap-frogging Vettel with a 1m25.167s a lap later.

12:03 Rosberg's latest run has kicked off in the mid-1m24s, which is as quick as any other car has managed to go so far, but 1.5s slower than the best from the Mercedes.

12:03 BEN ANDERSON: "Big support in the grandstands for new Spanish F1 driver Carlos Sainz Jr.

"The son of Spain's celebrated World Rally champion received loud cheers every time the Toro Rosso took to the track.

"Sainz managed to perform several practice starts while I was down in the pits.

"It's funny to think that things were so bad for the Renault-powered teams in testing last year that Daniil Kvyat hadn't even attempted a start until his first race in Melbourne..."

12:04 Having moved the Williams up the order, Bottas is back in the pits. Once again, Rosberg's Mercedes is alone on track.

12:19 No sign of let-up from Rosberg. He's up to 76 laps for the day, and his pace has slowed to low 1m25s now.

12:27 Sainz heads back out - while we've heard reports that Ricciardo's last run this morning came to a smoky end, and that's probably why we haven't seen the Red Bull for a while.

Sure enough, here's evidence of the Red Bull's plight from earlier.

12:31 The first few hours of 2015 testing certainly haven't given Mercedes much to worry about yet.

Rosberg's lap count: 84
All other teams combined: 98

12:32 Sainz improves by two tenths with a 1m25.836s, so he's just 0.072s adrift of Vettel's best in the Ferrari now.

12:33 Another improvement for the 2014 Formula Renault 3.5 champion, and now Sainz is above Vettel in the standings with a 1m25.327s.

12:35 Bottas joins Sainz and Rosberg on track, as Williams is about to head into double figures for day one in terms of laps.

12:36 Vettel re-appears after a long spell in the garage for the Ferrari. It didn't sound great heading out onto the track though.

12:36 If you want a refresher of all the events at Jerez so far today, including results and halfway-point lap counts, here's our morning round-up:

Jerez test day one am: Rosberg sets commanding pace

12:37 We have a car within one second of Rosberg's best: Bottas moves up to second in the Williams with a 1m23.906s. That puts him 0.8s adrift of the Mercedes.

12:40 Vettel sets a new personal best for the day, but it's not enough to move the Ferrari up from sixth in the standings.

He makes amends a lap later, going third with a 1m24.279s.

12:44 Bottas has now settled into mid-1m25s, while Vettel is quickly falling away into the 1m26s after setting his best lap.

Rosberg continues to notch up the laps, currently running in the 1m26s as he completes his 94th of the day.

12:45 Vettel picks the pace up again, and his 1m24.000s means he joins Bottas in getting inside one second of the pace set by Rosberg.

12:51 Bottas back into the pits after a longer run. He's racked up 19 laps now in the FW37. Only Rosberg left out there at the moment. He's almost made it to 100 laps...

12:53 Rosberg completes his 100th lap of the day in the Mercedes, and it's not even 2pm yet... Sainz has decided to join in the fun in his Toro Rosso.

12:58 Rosberg is back in the pits, leaving Sainz the Jerez circuit to himself. The Spaniard is lapping in the 1m27s at present.

13:04 Vettel heads back out in the Ferrari. With just 17 laps completed, Ferrari is lagging way behind Mercedes on mileage. Only Fernando Alonso's McLaren-Honda has completed fewer laps so far.

13:05 A couple of updates from JONATHAN NOBLE down in the paddock:

"Ricciardo has just headed towards the Red Bull garage in his overalls, so he may be heading back out soon.

"There's still a big empty slot behind the pits where the Lotus trucks should be, so the E23 is not here yet."

13:06 Vettel leaps to the top of the times for Ferrari. First man into the 1m22s and a tenth quicker than Rosberg's best effort so far

13:07 Vettel's pit board suggests he has three laps left on this run.

13:08 Both Vettel and Rosberg have gone faster than last year's fastest time overall from the Jerez test. The fastest in 2014 was a 1m23.276s.

13:08 Vettel's next lap is a fraction faster again. The four-times world champion has lowered the benchmark to 1m22.958s.

13:09 Vettel returns to the pits having lit up the timing screens on that run. All quiet on the track in Jerez for now.

13:18 JONATHAN NOBLE reports from the pitlane that Ron Dennis is in the McLaren garage surveying the MP4-30. It's not been out much, but things seem to be going more smoothly for Honda than they did in Abu Dhabi.

13:21 There are doubtless a lot of very knackered mechanics in the pitlane right now, as the build-up to launches and tests are the toughest time of the year for those creating the cars.

Our anonymous F1 insider the SECRET MECHANIC has been sharing tales of how the cars seen at launches might not be quite all they seem, and just how it feels when a driver shunts the car you've spent all winter finishing:

Secret Mechanic: All is not as it seems pre-season

13:21 Bottas heads back out onto the circuit in the Williams, so the track wakes up again after a bit of a lull.

13:28 Vettel and Sainz join Bottas out on track. Bottas is on a longer run and lapping in the 1m26s at the moment.

13:34 Vettel back in after a short run. The Ferrari has racked up 23 laps now. Sainz and Bottas still rolling round. Both are lapping in the 1m25s at the moment.

13:39 Red Bull is back in action this afternoon after a long delay. Ricciardo's morning run came to a smoky end, and the team took power tools to the car around lunchtime.

13:41 Ricciardo pressing on now in the RB10. A big wiggle as he comes out of the final corner before setting a new personal best time and then the fastest first sector of all so far...

13:41 Interesting to compare the McLaren-Honda performance so far with where everyone was on the equivalent day last year. Alonso has managed six laps, with a best time of 1m40.738s.

That's better than both Caterham and Red Bull managed (four laps between them, no time registered) and also Sauber (seven laps, with a best of 1m42.257s) but well off where others were. Bottas, in the Williams, for example did seven laps with a best of 1m30.082s.

Obviously, it's still very early days yet for Honda.

13:42 Ricciardo goes third fastest on the next lap. The Australian breaks into the 1m23s now and splits Rosberg's Mercedes and the Williams of Bottas.

13:46 Ricciardo has backed off over the last two laps of his running - dropping back to a 1m32.7s last time through. Rosberg is back out and lapping in the 1m24s. Bottas has also rejoined the action.

13:50 Ricciardo is back in the pits now, having whacked in another 1m24s lap before he did so. Rosberg and Bottas are currently trading blows in the mid-1m24s.

13:55 Pacesetter Vettel is back out in the Ferrari SF15-T and straight into the 1m24s. He's sharing the circuit with Rosberg, Bottas and Ericsson.

13:59 Vettel manages a 1m23.5s lap before diving back into the pits. No long runs yet from Ferrari, but encouraging pace from James Allison's first full car for the Scuderia.

14:00 The fact the new Mercedes has racked up over 100 laps already today will have come as an unwelcome shock to the other teams present at Jerez.

But one observer who seems particularly surprised is Rosberg's father and 1982 F1 champion Keke Rosberg, as one paddock snapper managed to capture.

14:04 Keke's son is now up to 122 laps completed in the Mercedes W06. He and Bottas continue to do similar laptimes - now in the low 1m26s.

14:10 The McLaren-Honda has been stuck in the garage for a while now. The team says it is currently trying to trace a problem with the MP4-30.

"Tracking down a niggly problem - which is taking some time. Hope to be out again before the end of the day."

14:17 It's still the Rosberg and Bottas show out on circuit. Rosberg's now managed 130 laps and his pace has gradually dropped away from the 1m25s to the low 1m26s. Bottas is doing consistent 1m26s laps.

14:19 Bottas pits, but for a few seconds there we had a 2015-high of five cars on track at the same time. Vettel, Rosberg, Ricciardo and Ericsson are out there at the moment.

14:22 Ricciardo has gone fastest of all through the first sector, although he's dropped a couple of tenths in the second part of the lap.

14:23 The Red Bull gets out of shape in the middle of the final corner, and Ricciardo crosses the line two tenths down on his best - so half a second adrift of former team-mate Vettel's pacesetting time.

14:24 Ricciardo is another half a second slower next time by, while Rosberg comes back into the pits with 136 laps to his name.

14:26 Here's today's lap count in full:

Rosberg (Mercedes) 136
Bottas (Williams) 51
Sainz (Toro Rosso) 41
Ericsson (Sauber) 40
Ricciardo (Red Bull) 34
Vettel (Ferrari) 31
Alonso (McLaren) 6

That's some decent recovery work from Williams, which hardly ran at all this morning.

14:38 Things have been quiet out there for a while now, but Sauber sends Ericsson back out to liven things up on track.

14:39 In stark contrast to this time last year, the day's running has been almost uninterrupted. Ericsson was responsible for a very brief red flag when he had a spin this morning, but he was able to rejoin and the green flags came out as soon as he got himself back to the pits.

14:42 As Ericsson enjoys having the track to himself and manages a slight improvement in laptime, here's a recap of some of today's headlines:

* Mercedes logs over 100 laps with Rosberg
* No sign of the new Lotus, which was only sent to Spain today
* Only six laps for Alonso in the McLaren-Honda so far
* Red Bull's morning running comes to a smoky end
* Vettel sets two laps good enough for P1 during a short run

14:48 While McLaren continues to work on what it earlier referred to as "a niggly problem", the team has Tweeted a picture of Ron Dennis and Eric Boullier speaking with the British press. JONATHAN NOBLE is there for us - it will be interesting to see how much the team's chiefs are prepared to say about the progress with Honda up to now.

14:50 Sainz breaks the silence on track, and he is followed out of the pits by current pacesetter Vettel.

14:52 There's a puff of dust from the Toro Rosso as Sainz has a huge moment coming out of the final corner which spits him way over the exit kerb. Cold tyres are probably to blame for that one, but he got away with it.

14:55 Vettel lowers the benchmark for the day. He's gone even quicker out front, getting down to a 1m22.690s in the Ferrari.

14:56 Vettel's time was set on medium compound tyres.

14:57 We have a red flag - only our second of the day. Vettel is still running, so it must be Sainz.

14:58 The timing screens suggest that Sainz was in the middle sector when he hit trouble.

15:11 The Toro Rosso has made its way back to the pits on the back of a flatbed truck. It's covered up, so it's still unclear what happened to cause the stoppage.

15:12 As the Toro Rosso is unloaded in front of the team's garage, the track is once again open.

15:13 Ericsson (softs), Bottas (mediums) and Rosberg (mediums) are first to head out as we are now into the final hour of today's running.

15:14 Current pacesetter Vettel is back out too, running on mediums.

15:15 Rosberg earlier had been sent out with flow-viz paint all over the front of his Mercedes steed, as this picture shows, as the Brackley-based team continues to get to grips with its new creation.

15:15 Ericsson runs wide on the exit of the final hairpin - clearly pushing - and he misses out on top spot by just 0.087s on that soft tyre flying lap.

15:17 Interesting news for McLaren fans:

@McLarenF1: Ron Dennis: "Our 2015 livery will change, but I'm not going to say when..."

15:24 Rosberg pits with 140 laps to his name for the day, runs straight through and starts lap 141.

15:25 Bottas is also on track, lapping in the 1m25s as he approaches 60 laps for the day.

15:26 Ah - we have some engine noise coming from the McLaren garage again. It was brief, but it's a sign of some progress being made on the troubleshooting front. Will Alonso get to add to his six laps so far?

15:28 Nothing on track at the moment, although the McLaren has been fired up again to make sure we're not sitting here in silence.

15:33 Ericsson and Rosberg head to the end of the pitlane together, but the Mercedes hangs back before following the Sauber out on track.

15:35 Rosberg passes through the pits and heads straight back out, while Ericsson has started a timed lap.

15:35 BEN ANDERSON: "Went to find out why pace-setter Sebastian Vettel had such a long delay in the Ferrari garage this morning. Turns out the car was suffering from a telemetry problem, which took a long time to fix."

15:40 Our top three - Vettel, Ericsson and Rosberg - are all on track at the moment.

15:41 Vettel is chasing the Sauber down, and he's gone ever-so-slightly faster, finding 0.070s to set a 1m22.620s.

15:42 Vettel passes Ericsson on that lap, setting a time four seconds quicker than the Sauber.

15:46 With 14 minutes remaining, there are four cars on track: Vettel, Ericsson, Rosberg and Sainz.

15:46 But on saying that, Rosberg heads into the pits. He's now clocked 148 laps on a remarkable first day for Mercedes.

15:46 And Rosberg rejoins the track again.

15:48 Vettel has now notched up 50 laps for the new Ferrari. So the team joins Sauber, Mercedes and Williams in the half-century club for today.

15:50 And Rosberg completes his 150th lap of the day. He's now in the pits.

15:51 EDD STRAW: "OK, Mercedes has already had the car on track before today on a promotional day, but to log 150 laps on the first official test day is absolutely outstanding. Looking strong."

15:54 Vettel, Ericsson, Rosberg and Bottas still on track with six minutes remaining. Vettel still has fastest time.

15:55 Looks like Rosberg was doing an aero run down the main straight.

15:58 Vettel does a practice start, with the rear of the car covered in aero paint.

16:00 And that's the chequered flag. Vettel and Ferrari top the first day of pre-season testing in 2015. Raikkonen did the same last year...

1 Vettel (Ferrari), 1m22.620s
2 Ericsson (Sauber), 1m22.777s
3 Rosberg (Mercedes), 1m23.106s
4 Ricciardo (Red Bull), 1m23.338s
5 Bottas (Williams), 1m23.906s
6 Sainz (Toro Rosso), 1m25.327s
7 Alonso (Ferrari), 1m40.738s

16:02 Here's the lap count for the day:

Rosberg - 157 laps
Ericsson - 73 laps
Bottas - 73 laps
Vettel - 60 laps
Sainz - 46 laps
Ricciardo - 35 laps
Alonso - 6 laps

16:13 Here's the full report from that intriguing opening day of 2015 running:

Jerez day one report: Vettel fastest for Ferrari

Keep an eye on AUTOSPORT tonight for all the reaction and analysis from the paddock, plus technical expert CRAIG SCARBOROUGH's low-down on the Mercedes W06.

AUTOSPORT Live coverage from Jerez resumes from 8am UK time on Monday morning. See you then.