1608: And that's your lot. The chequered flag has waved and the session is over, with Sebastian Vettel's 1.23.315 from this morning putting him on top for the second day in a row. Jaime Alguersuari was two 10ths slower with his 1.23.519 and Fernando Alonso's Ferrari was third, 0.6 secs down. Jenson Button finds himself down in eighth, more than a second and a half off the pace. McLaren seemingly have a bit of work to do. Many thanks for your company and all your texts and tweets, it's been a lot of fun. Coverage continues in the same place here on Sunday morning.

1556: We're into the last few moments of the session now, with Vettel still fastest ahead of Alguersuari, Alonso, Barichello, Heidfeld, Kobayashi, Rosberg and Button. Vettel and Rosberg are both now doing practice pit stops on each lap. Two minutes left.

1551: I think Nick Heidfeld must have read what Ted Kravitz said earlier - he's improved to eighth place with a 1.25.013. Vettel's back out too with nine minutes to go.

BBC F1 pit-lane reporter Ted Kravitz in Barcelona: "Mark Webber, who is taking over the Red Bull for the final two days of the test, has just arrived in the team's garage, and is discussing the work so far with his team-mate."

1548: Vettel's stint comes to an end as he pits the Red Bull and is pushed back into the garage by his mechanics. Time for a quick sprint before the end perhaps?

BBC F1 pit-lane reporter Ted Kravitz in Barcelona: "The best lap of the day by Nick Heidfeld was a 1:25.013 on the last lap of his short run. Renault have been concentrating on pure pace at the end of the day and that's put the German eighth overall, 1.7 seconds behind the Red Bull. I think Renault expected a bit better than that."

1543: Alonso can't quite match his fellow Spaniard's time, but a 1.23.978 slots him into third place. Just 17 minutes left in the session now, with Vettel and Rosberg continuing their marathon stints and Barrichello out too. Things on the track are heating up, even though there are grey clouds overhead.

1539: Now here's some news - Jaime Alguersuari has just posted a 1.23.519 which puts him second-fastest. He's just two 10ths off of Vettel's time in the sister car, and sending out a strong message to his teammate Sebastien Buemi who recently stoked the fire of competition between the pair. Your move, Mr Buemi.

BBC Sport's Andrew Benson: "To Kate, on the moveable rear wing - the drivers will be able to use the device whenever they like in practice and qualifying. But in the race they will only be allowed to use it under strictly regulated conditions. Currently, the plan is that a driver can use the wing if he is within a second of the car in front at a specific reference point on the track before the straight that has been designated for its use. On that straight, there will be a point where the wing can be deployed, which for now is expected to be 600m before the corner that ends it. Governing body the FIA will alter these parameters until it has reached what they think is the optimum - the idea being to make overtaking possible between cars of comparable performance but still a challenge."

1530: Sebastian Vettel looks like he won't be threatening his fastest lap from the morning session - he's resumed his long-running stint and is lapping in the early 1.28's. Nico Rosberg has also completed a vast number of laps today, and pops in for some fresh tyres as his times fade to 1.32's.

Kate Deans on Twitter: "Will the teams be allowed to open the rear wing whenever they want in qualifying sessions?" Interesting question Kate, BBC Sport's Andrew Benson will provide you with an answer in just a moment...

Renault on Twitter: "Nick is well into his programme now with 24 laps complete. Mostly short runs as he tries out new and scrubbed tyres."

1519: Barrichello's Williams and Alonso's Ferrari were lapping in close proximity for a while, but now the Spaniard has left him for dust and is lapping consistently in the 1.27's. Someone else who's got the bit between his teeth is Kamui Kobayashi - who posts a 1.24.243 that puts his Sauber third quickest behind Vettel and Barrichello. Impressive stuff. Vettel's Red Bull has now been fixed and he blasts back out onto the circuit. Can he lower his lap time further?

Mercedes GP on Twitter: "100 laps on the board for Nico as he continues with his race simulation. Good practice work on the pit stops this afternoon for the guys!"

1508: Tonio Liuzzi's just improved his best time to 1.27.044 in the Hispania - which puts him in 11th position overall and ahead of Heidfeld's Renault and Glock's Virgin. It doesn't look like anyone is going to be able to touch Vettel's lap at the moment, but we still have just under an hour to go in the session.

1454: Horner, we have a problem. Some glum-looking faces in the Red Bull garage now as Vettel is out of the car which is then surrounded by mechanics. Kobayashi puts his Sauber up to seventh with a 1.25.059.

1448: The Spanish crowd make some noise as their hero Fernando Alonso emerges once again. He's on form too - a 1.24.449 puts his Ferrari into third, but only for a moment as Jaimie Alguersuari's Toro Rosso pips him with a 1.24.432. Red Bull's sister team are looking pretty fast as Button, Heidfeld, Rosberg and Kovalainen all head out on track - the Finn set for a long run.

Ted's snap of the Red Bull pit lane crew

BBC Sport's Sarah Holt in Barcelona: "Ted is contemplating a sideline career in photography after snapping this beauty of Sebastian Vettel's Red Bull passing the team pit wall for me. If you look closely you can see that team boss Christian Horner is favouring his brown deck shoes over the regulation Red Bull trainer. And for those of you desperate to know, there was NO foot jiggling from the Red Bull boss."

1435: The stricken Force India has now been returned to the pit lane, and we're underway once more... Kamui Kobayashi and Heikki Kovalainen head out, which I guess means that's the last we'll see of Ricardo Teixeira for the day.

BBC F1 pit lane reporter Ted Kravitz in Barcelona: "Sebastian Vettel's race simulation has been suspended with 29 laps still to run thanks to the third red flag of the day courtesy of Paul di Resta, who spun his Force India off into the gravel at Turn One. We expect Red Bull to resume shortly. It's a bit annoying for them, though, because it won't give them a truly representative picture of what will happen to the tyres during a race."

1430: Ah that'll be why - Paul Di Resta's Force India has made it's way into the gravel on Turn 1. Bad news for the young Scotsman who's set the fifth-fastest time so far - a 1.25.194. The recovery truck is on it's way, as the pit lane takes a little breather.

1428: The RED FLAGS are out for the third time today - I'll provide you with a reason why shortly, nobody seems to know at the moment.

Ferrari on Twitter: "Still some work to do in the car but it should not take too much time to have Fernando running again."

1423: Sebastian Vettel is even quicker on his third set of tyres and is now lapping in the 1.28's. Rubens Barrichello is back out in the Williams as Jenson Button pits his McLaren and is wheeled back into the garage. No sign of Alonso in the afternoon session so far...

BBC Sport's Sarah Holt in Barcelona: "I have had a quick word with Sauber technical director James Key to ask just how much we can tell from testing times, with Kamui Kobayashi six seconds off the pace for Sauber after completing more than 60 laps in the morning. 'It's very difficult to read anything into lap times at the moment and we're not taking too much notice of them,' said Key. 'Our work this morning was race preparation work so we were on very high levels of fuel and working through most scenarios in race set-up. Running a race level of fuel you will be five seconds off the pace compared to someone who maybe does a 20-kilo run on a new soft tyre.' Key was cautiously optimistic about Sauber's progress, saying the team were 'OK for now'. I'm also optimistic after one of the hospitality ladies gave me a paper cup filled with mini Swiss chocolates as my parting gift from the team's motorhome."

1413: Timo Glock's just set his fastest lap of the test so far, a 1.28.972 that is good enough for 12th spot. Only Kobayashi's Sauber and Teixeira's Lotus are slower, with the former working with heavy fuel loads thus far. Vettel's just pitted for the second time during his marathon stint, his tyres lasted 15 laps this time around and the Red Bull crew provide him with a perfect practice pit stop.

BBC F1 pit-lane reporter Ted Kravitz in Barcelona: "Here's a comparison between the pace of the Red Bull and the McLaren, albeit an unscientific one as we don't know exactly what tyres each are running. Sebastian Vettel, with 49 laps of a race simulation remaining, has just lapped in 1:29.4 whereas Jenson Button with only 18 laps left of his 20-lap run is slower on a 1:30.2. We don't know how much extra fuel Button has on board but it does look like the McLaren is still significantly slower than the Red Bull at a time when they are on comparable programmes."

1403: Button's on a longer run now and has 17 laps to go according to his pit board. Most drivers seem to be on long stints - Vettel, Heidfeld, Rosberg and Teixeira are all out lapping the 2.8 mile track, with the Lotus on a fresh set of hard Pirellis.

Toro Rosso's Sebastien Buemi on Twitter: "Barcelonaaaa!"

BBC F1 pit-lane reporter Ted Kravitz in Barcelona: "Sebastian Vettel and Heikki Kovalainen are the only two drivers who aren't using their moveable rear wings on the straights this afternoon and that's because both the Red Bull and Lotus are doing race simulations. If they were in a race they would only be able to use the rear wing if they were less than a second behind another driver. With 60 laps to go in his race simulation, Vettel is solidly in the 1:30s, which is a very respectable time given the fuel he had on board. For the record, Hispania are not using the wing either because they do not have one yet."

1354: A little breaking Alonso news for you - the double-world champion is tipping Red Bull to once again be the team to beat at the start of the new season, whenever that may be. You can read what the freshly-shaven Spaniard had to say by clicking here.

1350: Vettel's lengthy stint is brought to a temporary halt just 10 laps in, when he stops for tyres. His first set seemed to be going off, with his times dropping to over 1.32 before he came in. The pit crew have a little kerfuffle around the rear of the car before he's sent on his way again.

1342: Better news for Button - he's wrestled his McLaren around the Circuit de Catalunya in 1.24.923, which displaces fellow Briton Paul Di Resta from fourth position. Vettel is now six laps into his stint and is lapping around the 1.30 mark - seven seconds slower than his earlier pace.

1336: As promised, here's Mr Kravitz's assessment of testing so far, as well as the latest on what the current situation in Bahrain is likely to mean for the sport.

1329: Timo Glock is doing some proper running now, although he remains a whole six seconds of Vettel's pace. The Red Bull racer is also back on track, and practices his starts at the end of the pit lane before setting out for another stint. According to his pit board it's going to be a long one too - 66 laps.

1321: Lots of you are asking about McLaren's pace, or apparent lack of it so far. BBC F1 pit lane reporter Ted Kravitz is in Barcelona and will have more on that for you soon. Paul Di Resta's Force India is currently the only car out on track at the moment, everyone else having decided to return to the pits for checks and tweaks.

1315: Jenson Button has just improved his time to a 1.25.950, good enough for seventh spot. Vettel's out again too, just for an installation lap before returning to the pits.

1310: Timo Glock is out first in the Virgin, closely followed by Lotus rookie Ricardo Teixeira (see 1058 update). Nick Heidfeld has also taken over Vitaly Petrov's Renault for the afternoon.

1307: Right, time to get going again. Don't forget you can get in touch directly if you have any questions - I promise we'll try to answer as many as we can. You have three choices too, you can Text 81111 and start your message with F1, tweet me @tombowker or tweet using the hashtag #bbcf1.

1220: Just a quick technical update for you. We've now managed to fix our auto-refresh problems, so from now on you should hopefully be able to sit back and relax and let the wonders of technology publish the updates for you.

1202: Well it's lunchtime at the Circuit de Catalunya, so I suppose it is for me as well. Sebastian Vettel will be happiest tucking into his pasta - the German is seven 10ths clear of the chasing pack with a best time of 1.23.315. The rest of the top 10 are Barrichello, Rosberg, Di Resta, Alonso, Alguersuari, Kovalainen, Petrov, Button and Liuzzi. I'm off to get a sandwich, be back soon.

1158: With not long to go until the lunch break, McLaren's Jenson Button is back out on track and posts a 1.27.027 that slots him into eighth place, 3.7 seconds adrift of Vettel's Red Bull. The 2009 world champion will be hoping for some big improvements on that time in the afternoon session. Nico Rosberg, meanwhile, leaps into third with a 1.24.730.

BBC Sport's Sarah Holt on Twitter: "Fernando Alonso has just spoken to the media while the mechanics work on solving mechanical issues that have halted his session. Alonso says: 'We expect Red Bull to be very competitive. But there is a lot to come from Ferrari as well so we'll see.'"

BBC F1 pit-lane reporter Ted Kravitz: "Red Bull look to have just run a qualifying session simulation. Sebastian Vettel completed another fastest lap of the test so far - he spent one minute and 50 seconds back in the garage in between quick laps for a change of tyres. All the mechanics were in their race suits working under the same conditions as they would be during qualifying, as were team boss Christian Horner and chief technical officer Adrian Newey on the pit wall. I would not expect that Vettel ran with qualifying level fuel as you would reckon on a faster time than a 1:23. We'll see whether Red Bull go for a race simulation later in the day."

BBC Sport's Andrew Benson: "In answer to Owen's question about McLaren's form, the truth is it is very difficult to judge at the moment. That goes for all the teams because of the uncertainty over tyre compounds and fuel loads, but even more so for McLaren, whose car has done much less running than most of the others. It's true that the perceived wisdom in F1 is that the Red Bull and Ferrari are the fastest cars, the order changing depending on who you speak to. But the McLaren simply hasn't done enough laps to come to any conclusions at all. That said, the contrast between them and their top-three rivals is stark so far. The Red Bull and Ferrari have generally run reliably and looked obviously quick. The McLaren has not."

Owen in Sandbach via Text (81111): "Very concerned about McLaren. Are they lacking in pace AGAIN with a new car? What's the general feeling amongst the teams & experts?" I can't vouch for what the teams are saying Owen, but I can get an expert's opinion. Andrew Benson is on the case...

1139: Sorry Rubens, I appear to have cursed you. Sebastian Vettel shoots to the top of the timesheets with a 1.23.315 on another qualifying-style two lap run. Seb is now a whopping seven tenths clear of the Williams, and the best part of two seconds ahead of everyone else - ominous pace from the Red Bull.

Lotus' Mike Gascoyne on Twitter: "Heikki out again, collector filter was blocked so problem fixed now. Ricardo will get his run after lunch now."

1128: Rubinho is showing them all the way - not only has Barrichello completed the most laps so far, he's just improved his own fastest lap to a 1.24.042. That benchmark is six tenths up on Vettel and over a second ahead of the chasing pack. A Williams renaissance this year would certainly mix things up a bit, wouldn't it?

Rizarazu on Twitter: "If Mercedes GP have been developing their car for so long why is it still so slow?!"

BBC Sport's Sarah Holt in Barcelona: "Fernando Alonso has just spoken to the media while the team tinker with his Ferrari so he can return to the track later. Alonso reports that the car feels good and that testing so far has been a bit of a surprise in terms of how reliable the car has been. It is generally accepted among the watching F1 fraternity that Red Bull still have the fastest car on track closely followed by Ferrari, which is how the 2010 season ended. Alonso said: 'There is completely zero information about the others but we all know that Red Bull should be ahead of everybody.' He added: 'There is a lot to come from Ferrari as well.' The Spanish double world champion also revealed that his progress on Saturday had also been upset by mechanical as well as electronic issues."

1116: Tonio Liuzzi's making progress in the Hispania, posting a 1.28.580. His potential teammate Narain Karthikeyan was only two tenths faster yesterday. Could the Italian be on his way to securing a seat for 2011?

Dan at Heathrow on Twitter: "I wonder what Renault's pace will be like today, I reckon they were sandbagging yesterday."

1112: It's Vettel time again. The world champion's Red Bull has been back in the garage for the last 90 minutes receiving some TLC from the team, but now Heppenheim's finest is ready for action again. He's not wasting any time either - two laps in and he's already up to second place with a 1.25.025.

BBC Sport's Andrew Benson: "In response to Zaki's question about running more than one car, the answer is that while teams would learn more if they ran two cars (as they used to, in fact), F1 teams now have an agreement to run only one car a day in testing. It's part of the sport's drive to keep costs under control. This is also why there is no in-season testing any more, when several years ago there would be tests between nearly all the races."

1058: Interesting news from Lotus this morning. After Heikki Kovalainen has finished his stint (he's currently 8th fastest with a 1.28.028), Angolan Formula 2 driver Ricardo Teixeira will get a 30-lap audition for a testing role with the team.

Zaki Mangalji on Twitter: "Instead of drivers taking turns with the cars, why cant teams run both their cars? Wouldn't it be more useful to run both cars?" BBC Sport's Andrew Benson will have the answer for you shortly Zakspeed. Mind if I call you Zakspeed ?

1045: Paul di Resta's got the hang of this hasn't he? He bangs in a 1.25.194 to go second only to Barrichello's Williams, albeit just over a second adrift of the Brazilian veteran. Alonso, Alguesuari and Vettel make up the top five.

Dougie in Crystal Palace via Text (81111): "Is it getting close to being a seriously worrying time for McLaren? The Red Bull and Ferrari were both fast straight out of the box and we've seen plenty of other cars top the timesheets. McLaren appear to have chosen a radical aero package, particularly the bodywork and rear of the car, but so far the times just aren't there. It looks awesome but is it quick?"

1036: Just a quick apology - it seems we are having some technical problems with our 'auto-refresh' function, so if you wouldn't mind manually refreshing your page while we fix things it would be very much appreciated.

1033: Sauber's Kamui Kobayashi has just started another long run - the Japanese driver is currently well off the pace in 10th, but has been driving with a lot of fuel on board. Nico Rosberg can't get enough running either - he's out for another stint after already completing 42 laps, with a best time so far of 1.28.001 that puts him in sixth spot.

BBC Sport's Sarah Holt on Twitter: "Tonio Liuzzi has done 20 laps in the 2010 Hispania car. The team are looking for good feedback from him as he chases a 2011 seat."

1015: Oh lordy, another RED FLAG - this time due to a detached piece of kerbing at Turn Two. Fortunately the marshals sort it out pronto and we're back underway without any fuss. Timo Glock's Virgin and Paul di Resta's Force India head out - with the rookie Scot lying in fourth place, 1.5 seconds behind Barrichello's Williams.

BBC F1 pit-lane reporter Ted Kravitz: "There's nothing wrong at McLaren even though Jenson Button has only done seven laps so far on Saturday. They are just between their set programmes. The early part of the morning was spent doing aero-mapping, where Button had to drive at constant speed down the straight with the moveable rear wing closed. McLaren mechanics are now working on the car's set-up in the garage. They are planning a lot of laps this afternoon. We will see if it's just a series of long runs or a full race simulation."

1008: Lots of questions are coming in about Bahrain and whether the first race of the season will be able to go ahead. BBC Sport's Gordon Farquhar has written a nice article entitled 'What happens if Bahrain is cancelled?', and his fellow sports news correspondent Tim Franks looks at the mixing of politics and sport.

0958: Rubens Barrichello's Williams is on fire this pre-season. The team officially launch their new livery on Thursday, but go-faster stripes won't be needed if he keeps this pace up. He's back at the top of the timesheets with a 1.24.264, demoting Alonso to second and showing the kind of pace Vettel's Red Bull did on Friday afternoon.

0954: It may be the weekend but the F1 gossip never stops. Take a look at the latest here, including a touching gesture for the recovering Robert Kubica.

0945: Vitaly Petrov has taken to the track in his Renault. Each time I see it I start humming Sam Sparro's 'Black and Gold', which isn't even a song I like particularly. It's catchy though.

0925: Sebastian Vettel is back out on track now and goes third with a 1m26.158s. His fastest lap on Friday was two seconds quicker, but many of the teams will be concentrating on working out their fuel loads and assessing tyre wear.

0920: Lots of questions coming in about Bahrain - you'll be the first to hear as soon as any decisions are made. Meanwhile, Fernando Alonso has already put this morning's electrical dramas behind him, going quickest with a 1:25.438, half a second quicker than Alguersuari's best effort. Looks like the horse is beginning to prance...

0911: Alguersuari has gone fastest, edging out Barrichello's time by two 10ths of a second with a 1m26.885s. It looks like the Toro Rosso might have some good pace this year. Most cars are popping in and out of the pits, and only Mercedes's Nico Rosberg has done a long run so far - he's fourth with a 1.28.545. Alonso's back out now too.

BBC F1 pit-lane reporter Ted Kravitz in Barcelona: "Fernando Alonso's Ferrari is being fixed in the garage under the watchful eye of Pat Fry, Ferrari's new head of race engineering and deputy technical director. Alonso is sitting in the motorhome with his manager, the car will be back in service soon. Meanwhile, a McLaren MP4-12C - the company's new sports car - has arrived in the paddock. Could it be Jenson Button's ride home after he finishes testing this afternoon? The car is proudly sporting its British tax disc - and the road tax for one of these cars is £205 a year."

Ferrari on Twitter: "Not a good start of the second day of the session. Fernando stopped on track due to an electric problem. Anyway, the issue has been solved. Fernando will run again very soon. Tyres and set-up changes are the main objectives of today's programme."

0857: Just getting underway again, so a quick times update for you - currently fastest is Rubens Barrichello in his Williams with a 1.26.910, just ahead of Toro Rosso's Jaime Alguersuari (1m27.101) and Force India's Paul di Resta (1m28.382s). It's starting to get busier now, with Button's McLaren, Rosberg's Mercedes and Vettel's Red Bull all out on track and the grandstands starting to fill up. No doubt there's a smell of beignets and coffee in the air.

0843: Bit more news on Alonso from BBC Sport's Sarah Holt in Barcelona: "The first red flag of the day fell when Fernando Alonso stopped out on track at the half-hour mark. The circuit's fixed cameras quickly zoomed in on the crimson Ferrari, which sat facing forward on the track, waiting to be hauled onto a flat-bed truck. Alonso also patiently waited with his arms folded behind his back at the back of a huddle of marshals. No sign of his winter beard, though. The intrepid Ted Kravitz has headed down to the Ferrari garage to find out why the so-far reliable F150th Italia ground to a halt."

BBC Sport's Andrew Benson: "To answer Jon in Romford's question, in theory the guy behind would win, because unless he was driving a Lotus, Virgin or Hispania, he would press his Kers button as well as using his moveable rear wing. It's worth bearing in mind, though, that the idea of the moveable rear wing is to make overtaking easier - not easy. F1's stakeholders still want overtaking to be difficult between evenly matched cars, just not practically impossible. And they will adjust how it is used until they get it right."

0836: Uh oh, the crowd won't be happy with this - RED FLAG - home favourite Fernando Alonso has stopped out at Turn Four. No signs of oil on the track fortunately, so hopefully it won't be long until the restart.

Jon in Romford via Text (81111): "So the car behind adjusts its rear wing to overtake, the car in front presses its Kers button in response. Hmm, who wins that race?" Very good question Jon, I have no idea. Fortunately our resident expert BBC Sport's Andrew Benson is sat alongside me, and will have an answer for you shortly.

BBC Sport's Sarah Holt in Barcelona: "Good morning. It's another brisk start to the second day of testing with temperatures hovering below 5C and plenty of team-branded woolly hats pulled down over ears. Saturday morning on the outskirts of Barcelona has lured cyclists out on to the hilly roads around the circuit, tennis players on mist-cloaked courts and an ever-growing crowd at the Circuit de Catalunya. A cluster of fans in the grandstand opposite the Ferrari garage greeted Fernando Alonso with a round of applause as he made his way out, while a few rows down a group of boys wearing red caps complete with horns kept watch for the Red Bull of Sebastian Vettel."

0800: Morning. It promises to be another fascinating day in Barcelona as the F1 testing enters its second day. Red Bull's Sebastian Vettel was quickest on Friday, going 1.111 seconds faster than home hero Fernando Alonso in his Ferrari. Will anyone have the pace to match the world champion today? Stay tuned..