Lewis Hamilton second in British GP practice behind Valtteri Bottas
Valtteri Bottas led Lewis Hamilton to a Mercedes one-two in second practice at the British Grand Prix but the Finn will receive a five-place grid penalty.
Bottas, who was quickest by just 0.047 seconds, has suffered the same gearbox problem that hit his team-mate at the Austrian Grand Prix last weekend.
Mercedes have changed the gearbox and, as it has not done the requisite six races, that means an automatic penalty.
The team say the problem is now "understood and contained".
It means the highest Bottas can line up for Sunday's race is sixth, even if he is fastest in qualifying on Saturday.
The 27-year-old was quickest in both practice sessions on Friday - although Hamilton set his fastest time on the slower 'soft' tyres because he had an off-track moment through the fast Becketts section on his qualifying simulation run on the super-soft tyres and then pitted to check for damage.
Ferrari's Kimi Raikkonen was third, 0.332secs behind Bottas, 0.128secs ahead of team-mate Sebastian Vettel.
The German is 20 points ahead of Hamilton in the championship after nine of 20 races heading into this weekend and Hamilton has made it clear he sees it as important to start clawing back some of that margin.
Hamilton would almost certainly have been quickest had he completed the lap on which he lost control at the final right-hander in Becketts - as many drivers did through the day.
He was on course to be about 0.3secs quicker than Bottas had he completed that lap.
And on the race-simulation runs later in the session, Hamilton was lap-for-lap about 0.2secs quicker than his team-mate - and the Mercedes had an advantage over the Ferrari.
"I definitely feel great," said Hamilton. "Driving around the track today has been incredible, seeing the fans, every time I go out I get to wave to the fans, and that is one of the greatest feelings when you see them and the response you get."
Red Bull had looked quick in the first session - splitting the Mercedes and Ferraris - but fell back slightly in the second session to be fifth and sixth, Max Verstappen ahead of Daniel Ricciardo.
Nico Hulkenberg impressed for Renault to set seventh fastest time, 11 places and 0.9secs ahead of team-mate Jolyon Palmer.
Felipe Massa's Williams was eighth, ahead of McLaren's Fernando Alonso, who is expected to have a new engine fitted overnight that will lead to the Spaniard starting from the back of the grid, and Force India's Esteban Ocon.
Raikkonen and Toro Rosso's Carlos Sainz were the other drivers to lose control at Becketts.
Raikkonen spun at the same place as Hamilton's incident, but managed to extricate the car from the gravel without any damage, while Sainz lost his car earlier in the sequence of bends and had a high-speed spin across the grass, losing a fair portion of the session as the car was cleaned up.