Toro Rosso's Daniel Ricciardo set the fastest time in a soaking first practice session at the British Grand Prix.
The Australian, a candidate to drive for Red Bull next season following Mark Webber's decision to leave Formula 1, headed Sauber's Nico Hulkenberg.
Williams's Pastor Maldonado was third ahead of Mercedes' Lewis Hamilton.
The wet conditions meant only 11 drivers set times and there were several spins in the tricky conditions.
But only one driver damaged his car, when Caterham's Charles Pic crashed at Club corner and broke his front wing.
The Frenchman's accident underlined why the teams and drivers were so reluctant to venture out in the rain.
Silverstone is very tricky in wet conditions, with puddles forming and rivers running across the track at certain corners.
Most of the teams have new parts for their cars and would not want to damage them, especially when the forecast for the weekend is dry.
Drivers sat in the pits for the majority of the session and only started to venture out in the closing 15 minutes.
McLaren driver Jenson Button said: "We have to apologise to the fans but it's really wet out there and it's going to be dry at the weekend.
"It's very easy to put it in the wall and we don't want to damage our new parts. If we do we'll be reverting to the old ones."
Button said he expected his McLaren team to have a better weekend after a difficult start to the season, but they would not be competing at the front.
"I think we should see an improvement," Button said. "Are we going to fight for a win or a podium? I don't think so, unless there's a miracle. But I think we can get some decent points."
Conditions are expected to improve ahead of the second session, which starts at 1400 BST, but it is not yet clear whether there will be any dry running.
Among the drivers not to set a time were championship leader Sebastian Vettel of Red Bull and his rivals Ferrari's Fernando Alonso and Lotus's Kimi Raikkonen.
Webber also did not set a time as speculation rages as to whether he will be replaced by Raikkonen or one of the Toro Rosso drivers, Ricciardo or Jean-Eric Vergne, who was seventh fastest.
Both Alonso and Raikkonen have admitted they need to have a good weekend in Silverstone and try to peg back some of the sizeable advantage Vettel has built up.
"All races are important from now on," Alonso said. "Especially being 36 points behind the leader we don't have much room to make mistakes to lose any more points.
"We need to stay calm. If we can finish in front of Sebastian, great, if not we try to finish as close to him as possible.
"Last year at Monza in early September I think I had 40 points or so ahead of Sebastian and it was not enough. And that was Monza. So it is not the ideal position but it is not the end of the world.
"Red Bull has been dominant here since 2009 so it will be an extremely close and challenging weekend - with Mercedes I'm sure very, very strong as well.
"It's an interesting weekend ahead of us but we approach it with confidence and knowing we have a good opportunity."
Hamilton said in his BBC Sport column: "What I want to do is get the car on pole position. That's what I'm here to do.
"I don't know whether we'll be in a position to do that, but I'm hoping so. We have some upgrades for the car but we don't know how they will compare with the ones the other teams have brought."