Conditions were wet from the outset, and steadily worsened. That meant that the 1m56.552s lap that Lotus driver Grosjean produced after 37 minutes proved to be the fastest anyone could manage all morning. Demonstrating how tricky the track was, Grosjean took to the grass at Becketts just after setting his benchmark time.
Daniel Ricciardo was among the initial pacesetters and remained second for Toro Rosso, 0.275 seconds behind Grosjean.
Lewis Hamilton led the home contingent for McLaren in third, followed by Sergio Perez's Sauber, Felipe Massa's Ferrari, and Red Bull driver Mark Webber, who also took several turns on top early on.
Although Kamui Kobayashi was only seventh in the times, he was among the most spectacular to watch on the wet track, managing to keep his Sauber on the road most of the time despite some slides. Team-mate Perez was one of several to have a harmless spin - although his incident could have collected Grosjean.
Marussia's Timo Glock and HRT test driver Dani Clos also looped their cars, but despite the conditions, everyone managed to avoid the barriers.
Unusually for a wet session, the majority of the field came out for some concerted running. Only the Force Indias and Ferrari's Fernando Alonso decided against flying laps.