As conditions improved slightly in the afternoon, the McLaren driver clocked 1 minute 56.345 seconds in the second session with Kamui Kobayashi of Sauber 0.129 seconds adrift.
Michael Schumacher posted the third fastest time fresh from his first podium finish at the European GP since coming out of retirement two years ago.
With rain drenching the Silverstone circuit, Bruno Senna of Williams spun off the soggy track and hit the barriers.
Championship leader Fernando Alonso was one of three drivers not to set a time in the morning with spray hampering visibility, and he was 10th fastest in the second session.
