Jenson Button joined BMW-Williams yesterday and, aged just 20, will become the youngest British driver ever to race in Formula One when the season starts in Australia on March 12th.

"I'm still on cloud nine at the moment," said Button, a teenager until last Wednesday. "I'm sure I'm ready for Formula One. I think this year's going to be a very interesting one for me."

Button, who takes over from the disappointing Italian former Indycar champion Alex Zanardi, will become the fifth youngest driver of all time after beating Brazilian Bruno Junqueira in a test "shoot-out" for the drive.

In Formula One they say that if you are good enough you are old enough and Button convinced Williams that was the case.

Team owner Frank Williams said that he had made the decision only shortly before yesterday's launch of the new FW22 car in Barcelona and the announcement of computer giant Compaq as the team's principal sponsor.

Button will now partner 24-year-old German Ralf Schumacher while Junqueira was named as an official test driver and will compete in Formula 3000 next season.

The previous youngest Briton in Formula One was Peter Collins who made his first appearance in a Grand Prix in 1952 at the age of 20 and 193 days.

Others have been even younger on their debuts - New Zealander Mike Thackwell was just 19 and 182 days old when he started the 1980 Canadian Grand Prix for Tyrrell.

Michael Schumacher was also 21 when he made his Formula One debut for Jordan at the Belgian Grand Prix in 1991 but the late Ayrton Senna was 24 when he first appeared on the grid.