SILVERSTONE, England (AFP) - German Nico Rosberg maintained his habit of clocking fastest laps in practice when he and his Williams team-mate Kazuki Nakajima delivered the best times in final free practice for Sunday's British Grand Prix.

The 23-year-old son of former champion Finn Keke Rosberg clocked 1min 18.889secs around the Silverstone circuit to outpace Japanese Nakajima by just two-tenths of a second.

This rarity of a Williams one-two at the top of the standings left Italian veteran Jarno Trulli pushed back to third, ahead of Friday's pace-setting German tyro Sebastian Vettel of Red Bull.

Championship leading Briton Jenson Button continued to struggle and was down in 12th place for Brawn GP, one place behind defending world champion and fellow Briton Lewis Hamilton of McLaren Mercedes.

The track was damp at the start following overnight rain, but dried gradually and a series of different drivers topped the times before Rosberg emerged on top.

The two Ferraris of Brazilian Felipe Massa and Finn Kimi Raikkonen were fifth and sixth fastest, but the session was not entirely indicative of the true potential for any of the drivers or their cars.