Button still on top at Jerez

The British driver, at the wheel of the hybrid Honda powered by this year's V8 engine, was the only man capable of lapping in less than 79 seconds.

Button was, for the first time, working alongside new teammate Rubens Barrichello, who finished second today, nearly four tenths behind the Briton.

Barrichello's running, however, was cut slightly short due to an engine problem.

"There was a minor problem with the engine so I had an engine change," Barrichello told autosport.com. "I could not run as much as I would have liked. I am not too worried about the familiarization of the tyres or the car, as next week there is a new car so it is a different thing.

"But it is very very different to drive a V8. I have to get used to it, I have to get that into my head. That's why it has taken a bit more time to get going, but I am .4 seconds slower than Jenson today so it is alright."

The Brazilian got a new seat fitted to his car, and although it was better than the one he tested last week, he was still not perfectly happy.

"We have a new shell here, I am happier with that, but I am still moving around," he said. "I sat up more but now instead of moving front to back then back to front, I am moving up and down! I have done the new seat for the new car already and I hope it will be different."

Ralf Schumacher was third quickest in the Toyota TF106, the German causing two of the four red flags which stopped the session today. The Toyota driver stopped on track early in the morning and then went off at the first corner in the afternoon.

Despite that, he finished ahead of teammate Jarno Trulli.

The Toyota duo were split by Williams drivers Alex Wurz and Nico Rosberg, who both caused a red flag each, the Austrian stopping on track in the morning and the German sliding off the circuit when the session was almost over.

Today's times:

Pos   Driver        Team                Tyres  Time     Laps
 1.   Button        Honda                (M)  1:18.795  92
 2.   Barrichello   Honda                (M)  1:19.288  61
 3.   R.Schumacher  Toyota               (B)  1:19.373  60
 4.   Wurz          Williams-Cosworth    (B)  1:20.187  77
 5.   Rosberg       Williams-Cosworth    (B)  1:20.323  49
 6.   Trulli        Toyota               (B)  1:20.333  75

All Timing Unofficial