Hamilton back on top but stops on track
Mercedes-AMG's British driver Lewis Hamilton drives during a practice session at the Silverstone circuit in Silverstone on July 4, 2014 - by Dimitar Dilkoff
The 29-year-old Briton, champion in 2008, clocked a best time of one minute and 34.508 seconds to outpace German Rosberg by 0.228sec on a warm and blustery day at Silverstone.
Spain's two-time champion Fernando Alonso of Ferrari was third fastest, seven seconds down on the pace-setter, ahead of the two Red Bulls of Australian Daniel Ricciardo and defending four-time champion Sebastian Vettel of Germany.
They were both more than a second behind on one lap pace but showed improvements in relative competitive speed on the long runs in the latter stages of the afternoon session.
Hamilton seemed to suffer a serious engine problem an hour into the 90-minute session when he stopped out on the circuit. "Engine stopped," he told the team by radio. "Says engine kill, no shifting."
Hamilton managed only 14 completed laps in the session compared to Rosberg's 35, but will have access to the championship leader's data after the session. Rosberg leads Hamilton by 29 points in the title race.
Finn Valtteri Bottas was sixth fastest for Williams – having missed the morning session when his car was run briefly for only three laps by Susie Wolff, the first woman to take part in a Grand Prix for 22 years – ahead of Briton Jenson Button in the leading McLaren.