The 22-year-old Brit was unveiled at a press conference in London on Monday.

And Button, who finished sixth at the French Grand Prix a day earlier, said: "I'm the most confident I ever have been, particularly after the weekend result.

"My aim is to be world champion - and BAR are a team I can do it with. I have a good opportunity of achieving my goal with them.

"I feel very happy in my ability and what I can do in the future. And if we achieve our aim, that's fantastic."

Button, seventh in the drivers' championship, was shocked last month when he discovered he would be axed by Renault.

The team opted to promote their 20-year-old French test driver Fernando Alonso to partner Jarno Trulli for next year's campaign - but Button believes he can learn the lessons of his time with Renault.

"Now, I'm so much more confident with the car, the speeds and working with different people," he said.

"I found it difficult at Benetton last year as I was young and it was all new.

"But I learned a lot driving-wise last season and now I've got the experience to be quick immediately next year."

BAR team principal Dave Richards shares Button's confidence.

He said: "It's a two-year contract with a two-year option - but I look at it as a four-year agreement as that's what it's going to be at the end of the day.

"And in that period I'm convinced Jenson will be world champion.

"It's a two-fold thing. It's how soon the team is truly competitive and how Jenson matures over the next four years.

"He's only 22, so I think we'll evolve together. He has an extraordinary potential and has already had three years in Formula One."