Spanish test driver Pedro de la Rosa was fastest in both hour-long sessions, ahead of Toyota's Brazilian reserve Ricardo Zonta.
While BAR's Jenson Button was the quickest race driver in the opening session, McLaren's Juan Pablo Montoya claimed that honour in the afternoon ahead of Finnish team mate Kimi Raikkonen.
Briton Button, who scored BAR's first points of the season when he finished fourth at last weekend's French Grand Prix, was only 11th fastest although his morning time remained the third best of the day.
Friday times can be misleading, with teams testing different set-ups, but Button has warned repeatedly that he expects McLaren to run away with Sunday's race, given their pace in testing at Silverstone and in recent races.
De la Rosa, who will not compete on Sunday, was nearly a second faster than any other driver in the morning with a lap of one minute 19.205 seconds while Zonta's best was 1:20.139.
He improved on that on a cold and overcast afternoon, clocking 1:18.530 compared to Zonta's 1:18.964.
Raikkonen, on pole at Silverstone last year and winner of three races this season, remains the clear favourite for victory since Montoya will be handicapped by having to start early in Saturday's qualifying.
The Colombian retired from the French Grand Prix while Raikkonen finished second after starting 13th.
Ralf Schumacher reinforced Toyota's hopes of a strong weekend with the fifth best time in both sessions.
Renault's Fernando Alonso, the championship leader after five wins in 10 races, sat out the morning session along with Italian team mate Giancarlo Fisichella but was seventh quickest in the afternoon.
Alonso leads Raikkonen by 24 points in the championship.
Ferrari's seven times world champion Michael Schumacher was seventh fastest in the morning and 10th in the afternoon.
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