SIR FRANK WILLIAMS admits that letting Mark Webber switch to Red Bull at the end of 2006 was a "mistake".
After two disappointing seasons with the British team in 2005 and 2006, the Australian moved to Red Bull, where in the past week he has won two grands prix from pole position.
"You could say we made a mistake," Williams is quoted by Austrian newspaper Kleine Zeitung.
"Our car was a disappointment, and we thought he was a part of that problem. Therefore, he was not our first choice (for 2007)," added the Grove based team's eponymous chief.
It is now expected that Webber, 33, will sign an extension to his current contract for the 2011 season.
Williams co-owner Patrick Head confirmed that he and Sir Frank were reluctant to pay Webber a high salary to stay on board in 2007.
"It wasn't that we thought he wasn't worth a decent salary, but we'd lost a major sponsor and we were going through some very tough times commercially," he is quoted by The Guardian.
"For the amount Flavio was asking, we didn't think we could build a car that would justify keeping him on," added Head.
The Briton also thinks Webber, the first Australian world championship leader since Alan Jones in 1981, has improved since leaving the Williams team.
Said Head: "He was very quick over a single lap but in our view he had an occasional tendency to make mistakes in the race and suddenly go off.
"In his first year with Red Bull he was pretty much the same. But in his second year with them we noticed that those in-race mistakes disappeared."
Red Bull Keen To Re-Sign Mark Webber For 2011
Red Bull would like to keep Mark Webber on board for the 2011 season.
After the Australian driver commandingly won the past two grands prix from pole position and took the lead of the world championship, it is being reported that Red Bull would like to extend his expiring contract.
Already under contract for next year is 33-year-old Webber's younger and highly rated teammate Sebastian Vettel.
"It is our desire to continue with Vettel and Webber," team owner Dietrich Mateschitz's motor sport adviser Dr Helmut Marko is quoted on Monday by Austria's APA news agency.
Marko indicated that Webber's run of top form has motivated Red Bull to keep him.
"It is important that both drivers are at a high level of performance, with each one pushing the other to excellence.
"They must be going to the limit, for themselves but subsequently for the car," added the Austrian former grand prix driver.
Marko acknowledged that the sort of form being shown by Webber could drive up his contract price.
"Of course, the management uses it for salary negotiations. But we know what he is worth to us."