Button was driving a 2005-specification car

The Englishman, returning to a BAR-Honda cockpit for the first time since the Chinese Grand Prix, left the other 11 drivers trailing.

Renault's Franck Montagny was second, with Toyota's Jarno Trulli third.

Button used a 2005-specification car, while team-mate Anthony Davidson tried an interim machine that complied with new rules to restrict engine power.

Davidson was five seconds slower than Button, giving some indication as to speeds expected next season, when the 2.4-litre V8 engines replace three-litre V10 units.

Toyota are now using Bridgestone tyres following their winter switch from Michelin.

Today marked the final session of BMW-Sauber's debut three-day test, with Nick Heidfeld once again given driving duties.

Team boss Mario Theissen was pleased with the new team's progress after finally seeing the culmination of his work in persuading BMW to buy Sauber.

He said: "This was a successful first joint test. It was important that we could run the BMW engine in the Sauber chassis at this early stage, in order to integrate all technical systems.

"This is the beginning of the testing season, and there is naturally a lot of work to be done.

"The co-operation at the track as well as the preparation of the interim chassis went very well - it was the first joint task of the new team."

Times:

1. Jenson Button (GB) 1 minute 14.111 seconds
2. Franck Montagny (Fra) 1:15.848
3. Jarno Trulli (Ita) 1:17.019
4. Ricardo Zonta (Bra) 1:17.440
5. Nick Heidfeld (Ger) 1:17.559
6. David Coulthard (GB) 1:18.392
7. Jose Maria Lopez (Arg) 1:18.428
8. Christian Klien (Aut) 1:18.471
9. Vitantonio Liuzzi (ITA) 1:19.065
10. Anthony Davidson (GB) 1:19.231
11. Mark Webber (Aus) 1:19.625
12. Nico Rosberg (Ger) 1:20.444