Williams could have signed Lewis Hamilton in 2004 but their former engine partners BMW passed up the opportunity, the F1 team's co-founder Patrick Head said.

Head told reporters that Hamilton and his father Anthony had visited the team's factory that year after falling out with backers McLaren while the Briton was racing in Formula Three Euroseries.

"They rang up and said 'can we come and see you?'," he recalled.

"And they came in and said '(McLaren boss) Ron Dennis has dropped us'.

"We were with BMW at the time and I think Frank rang (BMW's then-motorsport director) Mario Theissen and said 'look, this guy looks as if he could be pretty good and whatever and he has come to us saying can we help him'," continued Head.

"I think Mario said they weren't prepared to provide any support and we weren't in a position financially where we could finance his racing.

"So much to Frank's annoyance (now), he could have had Lewis in a Williams," said Head, a co-owner of the former champions who now have Toyota engines.