British GP: Hamilton unsure if Williams or Ferrari will lead chase

Ferrari established itself as Mercedes' main rival in the early part of the season, with Sebastian Vettel winning the second race of the year for the Italian team.

But Ferrari has lost out to Williams in the battle to be best of the rest at the last two grands prix, partly due to problems for the Scuderia and also because of progress being made with the FW37.

Hamilton expects another weekend of battling with team-mate Nico Rosberg at the front, but he believes the battle behind is too close to call.

"It's going to be a very hard weekend, and Nico's going to be very quick," said Hamilton at Silverstone on Thursday.

"I can't say who is going to be our main competitor this weekend, it could be Williams, it could be Ferrari.

"I'm hoping we have a race where we can actually just fight - one year it's been difficult for Nico with a car issue and one year for me [in 2013 and '14]."

Williams driver Felipe Massa, who took his first podium of the season last time out in Austria, expects his team to continue making progress this weekend.

"We had good pace [in Austria] and maybe we were missing one or two tenths to Ferrari," said the Brazilian.

"We're working so hard to get closer and maybe get similar, or hopefully, even faster than them.

"We've definitely been more competitive in the last two races than all the other races until Canada.

"It shows we are getting better, and I'm really looking forward to being competitive here again and being in a position to fight for another podium.

"We are also improving the package that we brought to Austria, some little things were not working like we expected.

"It's not that anything was wrong, but some things that we understood needed some little changes, which I expect to work better."