Button signs for Williams

Button released a statement on Thursday, prior to BAR's claim, where he expressed his delight at returning to Williams who he believes will give him his best opportunity to clinch the world championship in the future.

"I am very pleased that I had the option to re-join the BMW WilliamsF1 Team where my Formula 1 career started," he said. "For the meantime, the 2004 season has my full focus and attention. Beyond this, I have every confidence that the massive investment in resources and the depth of talent at WilliamsF1 and BMW provides the best platform for my future ambitions to be a World Champion."

Team boss Frank Williams was under the impression that BAR's option had expired and that Button was free to leave. He told BBC Radio Five Live: "He has been under option to his present team BAR for some time. The option expired recently and Button's management called us to say that the option was no longer valid and would we be interested in his services - and of course I reacted as you might expect me to.

"I think they (BAR) probably wanted to take up the option but whether they've executed or not will come out in due course."

Williams added that Button was more than capable of winning the championship if the team gives him a competitive car.

"If we give him a good enough car, most certainly yes," he said. "He's on a strong upward path, every drive he improves. We've always believed an outstanding measure of a great world champion driver is the smoothness with which he drives and the infrequency of his accidents."

If Williams pull off the move Button will join Australian Mark Webber who concluded his deal with the squad last month. The two replace Juan Pablo Montoya who heads to McLaren and Ralf Schumacher, who will take up a seat at Toyota.