Sebastian Vettel led Mark Webber in a Red Bull one-two in the first practice session for Silverstone's final British Grand Prix.
Webber had been in front for much of the morning, but a late charge from Vettel saw him slip ahead by 0.282 seconds.
The two Brawns took third and fourth, 0.8s down on Red Bull's pace, with Fernando Alonso completing the top five for Renault.
Unsurprisingly the session was overshadowed by the political storm erupting in the paddock following FOTA's announcement last night that its teams will start a breakaway championship in 2010. But with a race still going ahead as planned this weekend, the drivers proceeded with business as usual.
After a slow start to the session with few cars on track, the pace quickened considerably at the mid-way point, as Webber put in a 1m20.865s lap and was soon joined in a Red Bull one-two by Vettel, who was 0.3s slower.
Those positions stood for five minutes before Brawn's Rubens Barrichello briefly went ahead by a tenth and then Toyota's Jarno Trulli lapped in 1m20.585s to take the top spot with just over half an hour to go.
But Red Bull supremacy was restored shortly afterwards, with Webber producing first a 1m20.234s, then a 1m19.682s to cement his first position. Again he was chased by Vettel, although the second-placed German was 0.422s adrift.
While Webber settled for his 1m19.682s and spent the rest of the session on longer runs, Vettel came out for a final spurt. His initial lap looked set to be fastest before he encountered Sebastien Buemi's Toro Rosso in the complex, but he made up for it next around with a 1m19.400s to take the top spot in the final minute.
Championship leader Jenson Button moved up to third late on, 0.015s ahead of team-mate Barrichello but 0.827s slower than Vettel.
Felipe Massa was sixth in the best of the Ferraris, followed by Trulli and Lewis Hamilton, with both McLarens running aerodynamic analysis paint on their front wings this morning.
Williams's Nico Rosberg was only ninth this time, while Force India showed promising form with 10th and 11th places.
Renault's Nelson Piquet provided the first major incident of the weekend when he had a high-speed spin at Copse, continuing with damage.
Timo Glock also went off the road, spinning his Toyota at Club, but likewise escaped unscathed, as did his team-mate Trulli when the Italian had an excursion at Becketts on his last lap.
Pos Driver Team Time Laps
1. Vettel Red Bull-Renault (B) 1:19.400 20
2. Webber Red Bull-Renault (B) 1:19.682 + 0.282 19
3. Button Brawn-Mercedes (B) 1:20.227 + 0.827 20
4. Barrichello Brawn-Mercedes (B) 1:20.242 + 0.842 29
5. Alonso Renault (B) 1:20.458 + 1.058 26
6. Massa Ferrari (B) 1:20.471 + 1.071 23
7. Trulli Toyota (B) 1:20.585 + 1.185 32
8. Hamilton McLaren-Mercedes (B) 1:20.650 + 1.250 26
9. Rosberg Williams-Toyota (B) 1:20.815 + 1.415 32
10. Fisichella Force India-Mercedes (B) 1:20.838 + 1.438 25
11. Sutil Force India-Mercedes (B) 1:20.913 + 1.513 22
12. Kovalainen McLaren-Mercedes (B) 1:21.029 + 1.629 22
13. Heidfeld BMW-Sauber (B) 1:21.103 + 1.703 24
14. Raikkonen Ferrari (B) 1:21.179 + 1.779 27
15. Bourdais Toro Rosso-Ferrari (B) 1:21.384 + 1.984 23
16. Glock Toyota (B) 1:21.386 + 1.986 32
17. Nakajima Williams-Toyota (B) 1:21.489 + 2.089 26
18. Piquet Renault (B) 1:21.525 + 2.125 30
19. Buemi Toro Rosso-Ferrari (B) 1:21.590 + 2.190 37
20. Kubica BMW-Sauber (B) 1:21.801 + 2.401 16
All Timing Unofficial