The young Englishman, who has been dropped by Renault in favour of their test driver Fernando Alonso, is expected to partner 1997 world champion Jacques Villeneuve next season.

Button is believed to be replacing Olivier Panis, who BBC Sport Online has learned is being tipped to join Sauber.

A delighted Button revealed that a number of teams had been after his signature and he admitted that BAR boss David Richards had been a deciding factor in his decision.

"I'm thrilled to be joining BAR," he said. "I had a lot of teams I was talking to about where I wanted to go next year.

"I've been flattered by the enormous attention I've received, as I've had a whole range of opportunities open to me.

"But one reason I've come here is because of David and what he's done with the team in the last six months. It's a team which will keep on improving."

The young star admitted that he was still shocked by Renault's decision to axe him.

"I was told the day after the British Grand Prix that my services were not required for next season," he said.

Consistent scoring

"Even though Renault was only an option, I was slightly shocked, as it's been a very good, positive season."

Button has scored 11 of Renault's 15 points this season and finished sixth in Sunday's French Grand Prix.

BAR boss Richards, who said he only firmed up Button's move after Sunday's Grand Prix, echoed his new driver's surprise.

And he revealed that Button has no binding contract with former team Williams, cited as one of the reasons behind his Renault release.

"I was staggered when I heard Renault were releasing Jenson," he said.

"And when I was made aware there was no binding issue between him and Williams, I immediately set about securing him."

Richards has no doubts that he has signed one of the most talented drivers on the grid.

"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 become world champion."

While Villeneuve is expected to partner Button, Richards said a deal had yet to be signed with the Canadian who has a year left to run on his deal.

"We are in discussions with him about what he wants in the future and what the team needs in the future from him.

"Contracts are one thing but you need to have people who want to be there. I need long-term commitment," Richards said.