Button, who has spent the last two years driving for BAR-Honda, made his F1 debut with Williams in 2000. He then spent two seasons with Benetton/Renault before joining BAR.

On Aug. 5, BMW WilliamsF1 issued a release stating that it had signed a contract for Button to drive for the team in 2005 and beyond.

"There has been a long-term relationship between the BMW WilliamsF1 Team and Jenson," team owner Sir Frank Williams said in the statement. "We have maintained that relationship until the present day, and I am delighted that one of the most talented drivers in Formula One has accepted the opportunity to return to the team."

On Aug. 6, BAR-Honda issued a release saying Button was still under contract to the team for next year.

"We are absolutely astounded to hear that Jenson thinks that he is leaving BAR for Williams next season," BAR team principal David Richards said. "Neither myself nor any other member of the BAR team has been contacted by Jenson to discuss this matter.

"Jenson is under contract with BAR for 2005 since we took up an option on his services only last month. At no time during the last few months has Jenson expressed anything other than his desire to continue working with BAR to achieve our collective goal of winning the World Championship.

"It is our intention to enforce our current contractual position with Jenson. Unfortunately, this is now a matter for the lawyers, and I have every confidence that the legal process will confirm that yesterday's announcement has not only been premature but also invalid."

Button is third in the Drivers Championship. He has scored points in all but one of the 12 races so far and finished on the podium seven times. The only race he failed to finish was the United States Grand Prix at the Indianapolis Motor Speedway, where he retired with gearbox problems.

Frank Williams is confident that Button will drive for his team next season.

"The BAR option was invalid and not exercised properly," Williams said in a press conference Aug. 6. "It all happened a few days before the German Grand Prix (on July 25.) Until then we had assumed that it was out of the question. It was a great surprise. It was an opportunity, and we went for it.

"We have a contract with Jenson, and we are of the opinion that BAR lost its opportunity to retain him. One fact is incontestable: Jenson wants and expects to drive for BMW Williams in 2005 and 2006."

BAR issued an ultimatum to Button's management company, Essentially Sport, requiring them to arrange a face-to-face meeting between Button and BAR executives by Aug. 9.

"We have been trying to talk to Jenson for days," Richards said. "He has a clear duty to all of those who have worked with him for the last two years to explain to them what is going on." Button met with Richards on Aug. 8.

"David is now in no doubt of my intention to return to BMW Williams in 2005," Button said in a statement. "My contractual position allows for this. Given the circumstances, the meeting was constructive, and I have also clarified that I am not moving for money, and my motivation is straightforward determination to win a World Championship. I wish my return to Williams would have been less acrimonious in light of the contribution I have made to BAR this year."

The dispute will now likely go to arbitration with F1's contracts recognition board in Switzerland.

Williams already has signed Mark Webber for 2005. He joins the team after two years at Jaguar Racing. Williams needs two new drivers for next season to replace 2000 Indianapolis 500 winner Juan Pablo Montoya, who is heading for West McLaren-Mercedes, and Ralf Schumacher, who has signed a three-year contract with Panasonic Toyota Racing.