Bruno Senna admitted he was possibly over-cautious in Q2 at Silverstone, but said after recent bad luck and penalties, he did not want to risk getting a grid demotion for a yellow flag infringement in the end-of-session rush.
Yellows came out in the final sector at the end of Q2 when Romain Grosjean spun his Lotus into the gravel at Vale. Senna said he was particularly careful and ended up 14th fastest, while Williams team-mate Pastor Maldonado went through to Q3.
"I've been getting some bad luck in the last few races with what's been happening on the track and punishments, and I didn't want to push my luck today," said Senna.
"It's a question of talking to Charlie [Whiting] and finding out what he wants - if he wants you to be safe or if he wants you to be very subjectively proving on your telemetry that you slow down."
He is confident Williams will be competitive whatever the weather in the British Grand Prix, and said his qualifying performance did not really hint at his potential pace.
"Unfortunately that's how it goes. This is a lottery and today we weren't the winners," said Senna. "I was driving very conservatively - I don't have many miles in the car in these conditions so I wasn't pushing as hard as I could.
"We can still have a competitive race tomorrow, it's just harder when you have to come from the back. It's very frustrating and once again I'm just out of position on the start."