Susie Wolff, making her F1 practice debut in place of Valtteri Bottas, went fastest very early on 1m 44.212s, but then her engine lost oil pressure and she had to pull off the track at Club. Soon afterwards team mate Felipe Massa put a wheel over the kerb exiting Stowe and spun his FW36 heavily into the opposite wall on the approach to Vale, ripping off the left-front wheel. He was able to walk glumly back to the pits after a terrible opening to the weekend when he'll start his 200th race.
Meanwhile, after a suspected ERS problem had cleared up, Rosberg easily headed Hamilton with a lap of 1m 35.424s as the Briton struggled to 1m 36.155s.
Ferrari provided the closest challenge to Mercedes, with Fernando Alonso lapping in 1m 36.263s, 0.839s off Rosberg. The Italian team tried a modified rear wing on the Spaniard's car partway through and he set his best time using it.
Daniel Ricciardo was fourth for Red Bull on 1m 36.623s but reported a problem with his RB10's gearbox midway through the session. He managed to get going again so it looks like Red Bull will get away with not having to change the transmission. Team mate Sebastian Vettel continued to struggle with his car and was sixth on 1m 36.921s, separated from the Australian by Kimi Raikkonen in the second Ferrari on 1m 36.703s.
Jenson Button took seventh for McLaren with 1m 36.963s, ahead of the Toro Rossos of Daniil Kvyat and Jean-Eric Vergne on 1m 37.175s and 1m 37.227s respectively. Kevin Magnussen completed the top 10 with 1m 37.231s.
Sergio Perez complained about his Force India's steering on his way to 1m 37.720s for 11th, whilst Romain Grosjean and Esteban Gutierrez forced their way into 12th and 13th near the end. The Frenchman's Lotus was all over the road as he recorded 1m 37.910s, as the Sauber driver did 1m 38.056s.
Daniel Juncadella, deputising for Nico Hulkenberg at Force India, impressed with 1m 38.083s for 14th, which put him clear of Giedo van der Garde who recorded 1m 38.328s whilst using Adrian Sutil's Sauber.
Jules Bianchi took 16th with 1m 38.917s for Marussia, as Massa's best of 1m 39.461s left him only 17th. Max Chilton was plagued with high-speed understeer on his way to 1m 39.814s for 18th in the second Marussia.
Caterham also had a troubled morning. Test driver Robin Frijns, sitting in for Kamui Kobayshi, spent a long portion of the session in the garage as the team investigated problems with his car, while Marcus Ericsson spun at Becketts and couldn't select first gear to rejoin. The Swede was 19th on 1m 40.597s, the Dutchman 20th on 1m 42.261s. Wolff, who managed one flying lap, was a disappointed 21st as Pastor Maldonado failed to set a time after his Lotus broke down early on.