F1 journalist Dan Knutson in Jerez: "More bad news for McLaren. Jenson Button pulled out of the garage and got just a few feet past pit exit when his car stuttered to a stop. The McLaren mechanics have gone out to push the car back in. That was to have been the car's eighth lap of the day, but it was not to be.

"On Tuesday, McLaren talked of making a 'massive progress'. But presciently racing director Eric Boullier, referencing the problems of the first two days of the test, also added: 'Sometimes you just open the Pandora's box and you pick up one [problem], and then another one is coming.' Looks like that box might have just been flung open again."

Lewis Hamilton is getting down to business on track, clocking a 1:23.633 which moves him up to second, one second shy of Ferrari's Kimi Raikkonen.

Marcus Ericsson in the Sauber pops into third with a 1:25.081, 1.881 seconds off the pace set by Ferrari's Kimi Raikkonen. Felipe Massa improves, too, moving into fourth a further tenth adrift.

Red Bull report that they have an ERS issue on Daniil Kvyat's car, which is why we've seen so little of him so far today.

Here's a snapshot of the day's headlines:

• Lewis Hamilton completes 44 laps, but a spin brings out the red flag

• McLaren and Jenson Button manage just seven laps after a lengthy delay because of a "trivial issue" with the oil levels

• Red Bull also struggle with Daniil Kvyat completing just four laps

• Marussia's hopes of competing in 2015 are boosted

• Force India say they will make the season opener despite delays with their new car

Romain Grosjean in the Lotus clocks a 1:25.146 to go third quickest, 1.946 seconds off the pace set by Ferrari's Kimi Raikkonen.

Kimi Raikkonen is out and about in the Ferrari, along with Lotus' Romain Grosjean, Toro Rosso's Max Verstappen and McLaren's Jenson Button.

Image source, Getty Images

There was a big gap between Jenson Button completing an installation lap early in the day and the 2009 world champion coming back out.

McLaren say they performed checks around the car to see if everything was working smoothly after yesterday's problems. They found a "trivial issue" with the oil levels but "it is performing well now".

Andrew Benson
Chief F1 writer

"Can McLaren-Honda build on their reliability breakthrough on Tuesday and put in a full day's running on Wednesday? That is the hope, after what racing director Eric Boullier admitted was the 'huge relief' of the 32 laps Fernando Alonso managed on Tuesday before being stopped by a water leak.

"The electrical problems that had plagued them for the first two days - and two days in Abu Dhabi last November - seem to be over. And the leak was caused by a 'third-party component' that was easy to fix, if difficult to get to because of the tight packaging of what is a lovely-looking car.

"Boullier reported that there were no issues with cooling, and that Alonso, who only ran on wet-weather tyres, had been very pleased with the car. 'The driver comments were very, very positive,' Boullier said. 'Fernando said the car is really reacting well, the car is really stable, and you could see a couple of times on the pit wall checking in Turn One, with Mercedes driving at the same time, that the car was really stable on the entry.' Jenson Button will be hoping he can at least equal Alonso's mileage on his final day in the car in Jerez."

With three hours gone, here's the lap count:

Lewis Hamilton: 44

Max Verstappen: 41

Kimi Raikkonen: 33

Romain Grosjean: 30

Marcus Ericsson: 25

Felipe Massa: 15

Daniil Kvyat: 8

Jenson Button: 4

Image source, Getty Images

Toro Rosso's Max Verstappen has the track to himself at the moment as we approach the three-hour mark.

Good work from Mercedes who are preparing to get Lewis Hamilton back out around 35 minutes after he stopped out on track.

F1 journalist Dan Knutson in Jerez: "If the Marussia team does indeed make a comeback it will have to hire some new staff. Pat Symonds says that quite a few former Marussia and Caterham people are now working for Williams."

Tom Clarkson
BBC F1 pit-lane reporter

"We don't have absolute confirmation yet, but Lewis Hamilton appears to have had a spin at the chicane. The car was facing the wrong way with mud on the left rear tyre."

Ferrari's Kimi Raikkonen improves to a 1:23.812, 0.893 seconds quicker than Max Verstappen in the Toro Rosso. Felipe Massa is third fastest, eight tenths further back with Lewis Hamilton fourth, 2.299 seconds off the pace.

Image source, Williams

Williams:, external Felipe currently basking in the Spanish sun.

And Jenson Button puts a time on the board! It's a 1:30.706, which is 6.8 seconds off the pace set by Kimi Raikkonen.

Lewis Hamilton managed 43 laps before his session came to an abrupt halt. Meanwhile, Jenson Button has headed out in the McLaren.

The Mercedes is back in the pits which means we're back under way in Jerez.

Mercedes:, external Bit of an intermission as the car is fetched from an unusual parking spot between T11/12. Just awaiting her return now...