Ahead of today's opening session, the air temperature is 14 degrees C, while the track temperature is 15 degrees. It is wet, very wet, indeed, it is also exceedingly cool. Welcome to Britain.

Tyre choices this weekend are hard (prime) and soft (option) however, it's unlikely that we'll be seeing much of these this morning.

While Karun Chandhok is in Heikki Kovalainen's Lotus, and Nico Hulkenberg is in Adrian Sutil's Force India, the man we're all looking forward to seeing is Daniel Ricciardo who is making his F1 debut this weekend with Hispania.

Talking of Lotus, the green and yellow cars are sporting a revised Caterham livery

The lights go green and with the rain having stopped just a few minutes earlier, Paul di Resta leads the way followed by Buemi, d'Ambrosio, Alguersuari, Glock and Ricciardo.

More and more drivers pour on to the track, while most of them are on full wets a number of drivers feel that inters will be sufficient soon… providing the rain holds off.

Ferrari is running a revised rear wing, the Maranello team smothering it in hi-viz flow paint. Lots of new bits on the McLaren including a new rear wing, new rear brake ducts and a revised suspension. Much of this, of course, coming courtesy of the FIA's ban on blown diffusers.

Ten minutes into the session, all but Heidfeld have been out. The timing screen shows di Resta as not having been out yet he was among the first.

D'Ambrosio is the first driver to come out for a second run, the Belgian posting a 2:03.001 in the Virgin.

Button comes out for a second time as Heidfeld also makes an appearance. The Englishman dives into the pits, performs a practice pit stop then heads off again followed by Alguersuari.

Rosberg posts 1:51.590, as Alonso, Webber, Barrichello and Schumacher head down the pitlane.

As Webber goes second (51.659), Alonso spins at Vale having got it wrong exiting Stowe. Schumacher goes third ahead of Button, Barrichello and d'Ambrosio.

No sooner has Button improved (51.041) than Webber posts a 50.032, the Australian (and his future) the subject of intense speculation this weekend.

As Alguersuari takes a unique short cut into the pits - losing the car and heading across the grass and gravel - Hamilton begins his first flying lap of the weekend. The McLaren driver subsequently posts 53.505 to go sixth as teammate Button goes quickest with a 49.651. Most drivers on inters now.

Despite improving with a 49.651, Button is far from happy with the handling of the car, the Englishman revealing that he's almost scared to put his foot down. Elsewhere, Hamilton improves to second with a 49.577.

Vettel splits the McLarens with a 49.390, the entire rear end of the Red Bull covered in hi-viz paint.

Lotus. Mercedes and Ferrari report that they are expecting rain in around 15-20 minutes.

Vettel and Kobayashi both run wide, the Japanese driver locking up at the back before heading off into the gravel. Moments later Perez takes a trip through the gravel in the Luffield complex.

Despite an off on his previous lap, Schumacher posts PBs in all three sectors, crossing the line at 48.388 to go quickest. Vettel now second ahead of Massa, Button and Hamilton.

At half time, with Petrov the only driver yet to post a time, it's: Schumacher, Vettel, Massa, Button, Hamilton, Rosberg, di Resta, Webber, Kobayashi and Alguersuari.

Lots of smoke coming from Vettel's side of the Red Bull garage, the German looking suitably concerned even though he remains in his car.

Williams running back to back comparisons with their diffusers, Maldonado with the new version and Barrichello the old.