Welcome to the third practice session for the Spanish Grand Prix. The teams have one hour of running ahead of them in which to make the final few tweaks to the cars ahead of qualifying this afternoon.

There have been some interesting developments since the last session. Lots of talk about the new hard tyres, which appear to have divided opinion with some drivers able to get more life out of the than others - that could be crucial on Sunday. Hamilton called it a disaster but Pirelli insist that, although it gives less grip, it will last longer in the race.

The session is underway. Petrov is the first man out on track.

The other talk overnight was about Ferrari's rear wing. The one they used yesterday was deemed illegal by the FIA for having a large gurney flap on the top of the wing. Ferrari claimed it was their new slot-gap regulator but the FIA said it was simply an addition to the wing.

Rosberg makes a mistake in the final chicane and so does Hamilton on their last laps. Both have now returned to the pits.

It's all gone a bit quiet now. All the cars are back in the pits having completed an installation lap.

Trulli heads out on track in the Lotus. He's got the entire 4.655 km of the Circuit de Catalunya to himself. His car is twitching around quite a lot, so clearly there still isn't much grip out there on the hard tyres.

The drivers are really struggling to get them up to the optimum operating temperature and that makes the car slide, which in turn causes excess wear. Cars that can get them up to temperature are actually better on them, which is why Toro Rosso's Jaime Alguersuari actually quite likes them while the Lotuses have been struggling.

Schumacher has joined the action. Meanwhile Karthikeyan is sliding around and complaining that his DRS is not working.

Kobayashi is currently fastest on a 1:27.826, but we know from yesterday that a soft tyre lap time is at least five seconds quicker than that.

Schumacher ups the pace with a 1:26.599, but Vettel, Webber and Massa are now on track.

Webber goes quickest with a 1:24.750, 1.6 seconds up on Rosberg. All laps have been completed on hard tyres so far and we know from yesterday that the softs are roughly 2.5 seconds quicker.

A huge fire on Heidfeld's Renault. He's out of the car very quickly but there is some serious damage to the car. The marshals react quickly and put the fire out.

The fire started at the back of the car and then spewed out of the front-exiting exhausts as well. We haven't seen something like that for several years in F1. It'll be a tough job to fix the car before qualifying.

Renault says: "Nick's car catching fire was not scheduled, cause being investigated"

Webber has now improved to a 1:23.846, Hamilton is second 0.669 off the Red Bull.

The last big fire I can remember was last year at Singapore when Kovalainen's Lotus went up in flames. Heidfeld's fire was pretty similar to that.

Vettel still hasn't set a time and his mechanics have his engine cover off and are having a good poke around. A possible problem for the championship leader.

Button improves to third but is still 1.294 off Webber and roughly 0.6 off Hamilton in second. Button was having problems with the balance of his car yesterday but was confident he could correct them today.

Schumacher sets a new fastest time on the soft tyres with a 1:23.057. He's about 0.8 seconds faster than Webber on hard tyres.

We're expecting soft tyre runs from the frontrunners any time soon.

Renault says: "Right hand exhaust temp was very high from when Nick left pits. It was thought to have been a sensor problem. Rather evidently, it wasn't"

Rosberg sets a 1:23.397 on soft tyres but his lap was compromised by Petrov's Renault in the final chicane. He was quicker than Schumacher in the middle sector.

Red Bull say Vettel's problem is not serious but his team are still poking around in his engine and he has only completed three laps.

Massa goes fourth fastest on the soft tyre but is still slower than Webber on the hards.

Heidfeld's Renault is being returned to the pits so the team can start assessing the damage.

Kobayashi goes third fastest in the Sauber, 0.612 off Schumacher which suggests he will be aiming at Q3 this afternoon.

Alonso is out on the soft tyres, as is Webber.

Alonso told he is going for five timed laps, which suggests he is not going for a quick lap as he crosses the line 1.2 seconds off Schumacher's pace.

Webber sets the fastest time yet with a 1:21.791. Impressive stuff from the Australian and the fastest time we have seen so far this weekend.

Vettel is still in the garage with five minutes to go but the team is putting the engine cover back on.

Hamilton and Button go third and fourth fastest, roughly 1.2 seconds off the pace. That suggests they are on a heavier fuel load than the Red Bull as Hamilton went quicker than that yesterday.

Alonso is in the garage after his car got stuck in sixth gear during his five lap run on soft tyres. He had a similar problem during practice in Turkey two weeks ago.

Vettel is now on track and about to start his first flying lap of the session.

Vettel had a huge slide on the exit of turn nine but was still quicker than Webber in the middle sector... and he goes faster than Webber by 0.084 seconds.

The session ends with Vettel on top after a last minute lap. Impressive stuff, but he was probably on lighter fuel than team-mate Webber as the Aussie stayed out longer on his soft tyres.

Schumacher was third fastest and 1.3 seconds off the Red Bulls. McLaren were some way off Hamilton's pace yesterday so I suspect they will be a bit quicker in qualifying.

Thanks for joining us for the final practice session. Make sure you check back this afternoon for coverage of qualifying and all the teams' and drivers' reaction.