Williams will switch to Cosworth engines next season, AUTOSPORT has learned, after believing its prospects for success in 2010 are best served with the independent engine maker.
Although the Grove-based outfit came close to a deal with Renault, high level sources at the French car manufacturer have revealed that Williams has now informed the company that it is no longer interested in a tie-up for next year.
With Toyota already having confirmed that it is ending its customer supply deal at the end of this year, it means that Williams has now settled on a switch to Cosworth.
Williams is refusing to confirm its engine plans until after the end of the season, but its engineering director Patrick Head praised Cosworth's efforts in preparing for its return to Formula 1.
"They are certainly very committed to it and working hard," he said. "They have been one of the options but we are not stating where we cast our final hook in terms of what is available to us until after the final race of the season. But I think our design office know what they are designing for."
Sources claim that one of the key attractions for Cosworth is the fact that the engine supplier will be able to re-tune its power unit until early next year - something no other manufacturer is able to do because of F1's engine freeze.
The tweaks could help ensure Cosworth's engine is competitive throughout 2010, which is why Red Bull Racing is also considering a switch to the power unit if it is unsuccessful in its bid to secure Mercedes-Benz power.
Head said that his team had chosen to finish its partnership with Toyota because it fancied a change of direction.
"We had a very good relationship with Toyota," he said. "We made a decision about two months ago that we wanted to go in a different direction and I think the reasons are not for public consumption.
"We haven't had any falling out so it's an amicable parting. There were a number of factors that caused us to make the decision but I don't think that the combination of the reasons we decided to make a change are not ones that we are prepared to share. But it was nothing that caused any shouting and screaming, we chose to change direction.
"Ross Brawn and the team showed that you can make an engine change on Christmas Eve and still produce a pretty competitive car but I don't think our design office would thank us for doing that and they will have a little longer than that to design the car around the engine."