Valtteri Bottas is back out and improves with 1:20.756 while Max Verstappen goes second quickest with 1:21.773. Bottas is on mediums while Verstappen is on softs.

DJ: McLaren need to give us some longer runs on the Mediums & Sorts asap. No more running on these hypersofts tyres. Show some race pace please.

A fair mix of compounds being used this morning. Mercedes are on the trusty mediums - they haven't deviated from them throughout testing - while Stoffel Vandoorne went out earlier with hypersofts on his McLaren.

Sergio Perez is out there now on ultrasofts and he sets a 1:26.129 as Sergey Sirotkin improves with 1:24.487.

We have another time on the board as Sergey Sirotkin does a 1:27.830 on softs.

Sebastian Vettel, on softs, heads out onto the track, completes his third lap of the morning before heading back in again.

We may not have seen much testing last week, but Vettel saw enough to believe Ferrari will be "very close" to Mercedes this season.

In comes Nico Hulkenberg after a bit of aero work and the track falls silent.

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Andrew Benson
BBC Sport’s chief F1 writer

At the end of testing last week, Lewis Hamilton held a news conference. It did not provide any ‘news’, as such. But there were a few interesting little snippets, which we will run through in this live text. Firstly, the world champion is less than enamoured with the new track surface that has been laid at Barcelona, at the request of MotoGP, which prefers smooth tracks. Not only has this flattened out some bumps, it has also changed the banking of some corners.

Hamilton says: “There are no bumps and I’m not quite sure why they did a resurface as I think it is a waste of money in general because the older the surface the more character there is in a circuit. They’ve smoothed a lot of it out so it has lost a lot of its great character like a track like Barcelona has. They’ve done it at many circuits and I guess it has something to do with MotoGP, so we have that fight. I love MotoGP but they hate us because we make it bumpy and we hate them because they keep getting us to have these big run-off areas.

“I always relate it to a house. If you go and buy a brand new house it’s got no character, it’s new. And if you go and buy and old house, older homes always have got a little bit of history and a little bit more character. So it’s the same thing with a track.

“When you go to a brand new circuit it’s got no history, you don’t have the greats that have driven it in the past. But I like a track that’s a bit more dated in terms of surface. Drivers in the drivers’ briefings are constantly complaining about bumps but you have to manoeuvre around the bumps, you can brake a little more offline or you can brake after or slightly before them. You have to set the car up to be a little bit better in terms of ride height, but that’s where the character of a circuit is. If you flatten it all out you’ve got corners but it’s missing something.”

Image source, Getty Images

Not a lot, thanks to the Beast from the East (I'm going to miss saying that now it's gone).

Lewis Hamilton finished with the fastest time of the week - a 1:19.333 that he achieved on the final day which was a pretty busy one after snow rendered the third day largely a write off.

Here's the full rundown of the fastest times from the first test.

1 Mercedes (Hamilton) 1:19.333 (medium tyre)

2 Ferrari (Vettel) 1:19.673 (soft)

3 McLaren (Vandoorne) 1:19.854 (hyper-soft)

4 Red Bull (Ricciardo) 1:20.179 (medium)

5 Haas (Magnussen) 1:20.317 (super-soft)

6 Renault (Hulkenberg) 1:20.547 (medium)

7 Williams (Stroll) 1:21.142 (soft)

8 Toro Rosso (Gasly) 1:21.318 (soft)

9 Force India (Ocon) 1:21.841 (soft)

10 Sauber (Leclerc) 1:22.808 (soft)

Everyone apart from Marcus Ericsson in the Sauber has been out for at least an installation lap now.

Valtteri Bottas is clocking up the miles - he's up to nine laps already.

Pete Chambers: Mercedes only running drivers for day one and not the rest of the test? Or are the line ups for Tues-Friday yet to be announced?

I believe they will decide their line up each day but they have generally worked with both drivers getting a run out each day (weather permitting!) so the only thing to decide is who goes in the morning and who goes in the afternoon.

Out goes Nico Hulkenberg for an aero-run.

He's got soft tyres and an aero rake clamped onto the rear of his Renault.

Rapid improvements from Valtteri Bottas as he lowers the benchmark to 1:23.126.

Installation laps ahoy before Valtteri Bottas kicks the day off with a 1:33.287.

He's on the medium tyres.

As expected, it's a busy start to the day as Stoffel Vandoorne leads Sebastian Vettel, Max Verstappen, Valtteir Bottas and Sergey Sirotkin out onto the track.

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Very pleasant in Barcelona today with air temperature currently 9C and track temps 20C.

Testing is now officially under way.

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The green light is about to go on so here's the driver line up for today and for the rest of the week...

Image source, Circuit de Barcelona-Catalunya

Andrew Benson
BBC Sport’s chief F1 writer

Image source, Getty Images

Last week, the Beast from the East and then Storm Emma hit Formula 1 in Barcelona just as it did the rest of Europe. The result was a truncated test, with limited effective running.

So the teams will be doubly keen to make this week’s four days at the Circuit de Barcelona-Catalunya count. They are all that separate their cars from first practice at Melbourne’s Albert Park in just over two weeks’ time. The forecast is good - with temperatures predicted to peak at a blissful 19C on Friday.

It won’t reveal everything. But by the end of the next four days, Formula 1 2018 will be beginning to take shape.

Good morning and welcome along to our coverage of the second pre-season Formula 1 test in Barcelona.

We didn't see a lot of testing action last week, mainly because the track looked a lot like this...

Image source, Getty Images

But what a difference a week (or five days to be exact) makes...

Image source, McLaren