A link-up with Sauber could end BMW's relationship with Williams

But BMW motorsport boss Mario Theissen, whose company has a deal with Williams until 2009, denies a deal to buy the Swiss-based outfit has been done.

"I have been assured by Dr Theissen the board will decide towards the end of this month whether they wish to proceed with purchasing Sauber," said Williams.

Williams said a BMW takeover of Sauber would not necessarily mean the end of his partnership with the German firm.

When asked on Friday whether BMW had purchased Sauber, Theissen said: "We do not have any agreement so far."

He added: "We had several meetings. We started to talk about engine supply earlier this year, talks are going on and I expect a positive result, which means an agreement, and we are looking at the end of June."

BMW, which currently supplies engines exclusively to Williams, began discussions earlier this year with Red Bull Racing and the Ferrari-powered Sauber team.

Red Bull subsequently signed a deal to switch from Cosworth to Ferrari for 2006, leaving Sauber to search for a new engine supplier.

Williams criticises BMW

"It depends what Mario offers us," said Williams, confirming that his British-based team had talked to other engine providers despite having several years of its agreement with BMW left to run.

Williams have won 10 races with BMW engines but have failed to take the title since their partnership began in 2000.

They won five constructors' championships and four drivers' titles when they raced with Renault engines from 1989 to 1997.

Their partnership with Honda between 1983 and 1987 yielded two constructors' crowns and one drivers' championship.