Ahead of today's sole free practice session the air temperature is 16 degrees C, while the track temperature is 16 degrees. Although it is dry and a lot brighter today, the threat of rain persists and many believe that it is inevitable that there will be a downpour at some stage today.

While Friday's are always fairly inconclusive, yesterday's sessions, particularly the second when there was little running, especially by the big guns, was even more frustrating than usual with teams unable to collect any useful data for the remainder of the weekend. That and the fact that they were saving tyres in case the conditions continued.

The lights go green and unsurprisingly there is a mad scramble to get to work, within moments there are thirteen drivers on track. Maldonado complains that the wind is picking up, particularly in Turn 1. Elsewhere, Ricciardo loses control of his Hispania and heads off on to the grass.

As most drivers head back to their garages having completed an installation lap, Rosberg stays out. Only his teammate, Michael Schumacher, has yet to make an appearance.

The camera closes in on Christian Horner's vacant seat on the pit-wall, the Red Bull boss no doubt continuing his row with the FIA over the shambolic rules appertaining to blown diffusers. Shortly before the session got underway, the sport's governing body went back on its decision to allow Renault to retain 50% throttle under open braking. A move that will anger all those teams using the French manufacturer's engines.

As Schumacher finally heads down the pitlane, teammate Rosberg appears to have a minor fire at the rear of his car as he arrives back at his garage.

Replay shows Schumacher's car running very, very close to the ground.

Ten minutes into the session, d'Ambrosio, Trulli, Kovalainen and Maldonado are back on track, however, the Finn warns that dark clouds are closing in. Moments later, Maldonado confirms that it is raining at Turn 15 (Stowe).

As the first times of the day are posted, Schumacher goes quickest with a 1:36.228, Alguersuari goes second ahead of Kobayashi and Perez. Schumacher spins in the arena section as the rain begins to fall just a tiny bit harder.

Sensing that the weather could totally compromise their plans most of the big guns come out in order to get in the one lap or so, only Hamilton and Vettel remain in their garages.

Webber improves to third (36.603) but remains 0.375s off Schumacher's pace. Next time around the Australian goes quickest (34.699) and Kobayashi second.

As Button goes fifth (36.404), Hamilton finally heads down the pitlane followed by Vettel.

Liuzzi is told that the rain shower has ended with no more expected in the next half hour. However, at that point it rains even harder causing most drivers to dive back into the pits. All except Hamilton and Heidfeld who opt to brave the slippery conditions, the German on the dry option tyre!

As Hamilton and Heidfeld return to the pits, Kobayashi heads down the pitlane, the Sauber driver the only man on track.

As Rosberg, Alguersuari and Buemi join Kobayashi, in the Red Bull garage Webber's car has been stripped right down at the rear… the Australian appearing to have a problem… and not a minor one.

With Rosberg and the Toro Rosso drivers posting the odd PB, it appears the rain has ceased. Indeed, the Mercedes (on options) goes quickest in the first two sectors, finally crossing the line at 33.044 to go quickest.

D'Ambrosio, clearly not using his mirrors, almost collects Buemi at Club, the Swiss driver making his anger quite clear.

In the Mercedes garage there are problems for Schumacher also, as many as seven crew members working on his car.

As Perez goes second (33.280), Vettel is on a hot lap, posting PBs in the first two sectors and a 34.984 at the line.

Alonso goes third with a 33.433 ahead of Sutil, Massa and Petrov. A 33.663 sees Vettel improves to fifth.

With 20:40 on the clock, Webber finally climbs out of his car, all but he, Schumacher, Alguersuari and Buemi are on track. Alonso goes second (33.227) and Vettel fourth.