Williams F1 team must improve its wet form - Valtteri Bottas

Bottas and team-mate Felipe Massa had no answer to the faster Nico Rosberg and Sebastian Vettel when rain began to fall at Silverstone, dropping from podium positions to fifth and fourth respectively.

Last year's Hungarian Grand Prix was shaped by a pre-race thunderstorm, with drivers starting on intermediate tyres, and there is a slight chance of rain again in Budapest this weekend.

"We really struggled even when it was damp," Bottas said of Silverstone.

"When the speed gets low we just lose a downforce.

"It is an area we really need to work on because we are so much slower than anyone in the wet.

"The car is not where it should be."

Massa noted that Williams' troubles in the rain are nothing new.

"For two years we're trying to understand why [the team struggle in the rain] which is not nice," said the Brazilian.

"If you see the difference in terms of laptimes we were maybe fighting with Mercedes [at Silverstone], they were one or two tenths quicker, no more than that, in free air

"In the rain they were maybe two seconds faster.

"Our car this year is like an evolution. Last year was very bad in the rain and this year is also.

"We don't know why yet. We just lose a lot of grip."