World champion Jenson Button drove a McLaren for the first time on Wednesday but like all new car owners, the Briton spent a lot of time adjusting his seat.

Button, who will drive alongside 2008 champion Lewis Hamilton this season was determined to improve his sitting position in the car before getting out to the track.

When he did get behind the wheel, he clocked a time of 1min 12.951sec, from a total of 82 laps, the fifth best of day which was dominated by double world champion Fernando Alonso who set 1min 11.470sec in his Ferrari.

"It was a long day. We finished up at about 1am last night (Wednesday) trying to get the seat right in the car," said Button.

"Because you obviously have it made in the mock-up but it is always different when you get in the car and when you get out on the circuit it is always a bit different to what you expected.

"So we have been doing a lot of work to make me comfortable in the car. Initially, I wasn't quite where I wanted it to be, I was sitting quite high in the car."

Button admitted he would have prefered more time on the track but refused to be fazed by Alonso's pace which was half-a-second quicker than Pedro de la Rosa in a Sauber in second place.

Michael Schumacher was third fastest in his Mercedes.

"In a way it would have been nice to get some more testing done, set-up work but this test was always to get used to the environment inside the cockpit, get used to working with the team and to run through all the checks that you always do at the first test," said Button.