Sir Frank Williams has admitted that his F1 operation has struggled since allowing Adrian Newey to walk away in a disagreement over the latter's involvement in the team.

Although there have been brief peaks since Newey's departure in late 1997, Williams has largely been on a downward spiral since the split, while the renowned designer has become the most successful penman in F1 history after helping to create championship winners for both McLaren and, more recently, Red Bull Racing. Prior to that, he had helped Williams to land drivers' titles with Nigel Mansell, Alain Prost, Damon Hill and Jacques Villeneuve.

Speaking in the latest edition of F1 Racing magazine, Williams concedes that he made an error of judgement in allowing Newey's talent to slip through his fingers.

"He wanted some shares that I didn't want to give to him at the time," he revealed, "[That] was arguably, with hindsight, a mistake. Adrian is quite a remarkable individual."

Williams' decline reached its nadir in 2011, when the team recorded its worst ever championship performance, ending the season in ninth position with just five points, despite employing the talents of Rubens Barrichello and reigning GP2 champion Pastor Maldonado.

Determined to pull out of the dive in 2012, Williams has allowed the experienced Barrichello to leave, replaced by Bruno Senna, while the technical team has also been overhauled. Although the team has lost former technical directors Patrick Head to retirement and Sam Michael to McLaren, it has picked up Mike Coughlan to fill the role, as well as appointing a new chief operations engineer in Mark Gillan and aerodynamicist Jason Somerville.

"I'm not an engineer but I've seen lots of good cars and lots of bad cars - and ours wasn't quick enough," Williams said of last year's FW33, "It was deficient in most of the areas that matter, but we were completely lacking in the most important one of all, which is aero. And probably a bit of horsepower. It just wasn't a quick car.

"The Renault engine gives us hope. We have three new technical people - one is our technical director, one is chief of aero and one is running the cars. They have different backgrounds coming from three different teams."

Despite the renewed sense of optimism at Grove, however, the loss of the last man to bring championship success to the team still haunts Williams.

"There's still a problem, [and] it's called Adrian Newey," he admitted, "There's only one of him."