Williams surprised to keep Rosberg for '09

Rosberg originally only had a firm contract with the Grove-based team for 2008, with options beyond that, but he decided to extend it for another season at the end of last year.

The German has also subsequently made it clear that he hopes to stay at the team even longer providing they can give him a quick enough car.

Speaking about Rosberg's decision to renegotiate his contract at the end of last year, Williams said: "I was a little surprised that he was happy to sign to stay. I feared he would go to McLaren, and I was a bit surprised he didn't.

"He could not have gone there this year, he had a fixed contract, but 2009 was going to be the worry. We had an option for 2009 but it was very tough terms, based on the constructors' championship. It was by no means guaranteed we would achieve it."

Rosberg had been one of the leading contenders to fill the McLaren seat vacated by Fernando Alonso at the end of last year - although a move there for 2008 would have meant Williams releasing him.

Williams has confirmed that McLaren did approach his team about buying Rosberg about of his contract, but made it clear they were not interested in selling him on.

"It was never a thought we entertained," he said. "We had an offer from you know who, of majestic proportions, but it was never ever discussed.

"Why would we give away the crown jewels? Why bother improving the car by one second if we then give away half a second with the driver."

Although Rosberg has indicated several times that he would love to have a long-term future with Williams, co-owner Patrick Head admits the onus will be on the team to prove they can give him the goods to fulfil his potential.

"If we go through the next year and a half and show no signs of being able to get ourselves seriously up to the front, then I am sure his long term interests will go elsewhere," he explained.

"He is definitely capable of winning races and definitely capable of winning championships, as he showed in GP2. But he is doing everything he can to help us get back into a competitive position."