The partnership between Jenson Button and the Brawn GP team which this season produced a fairytale world championship triumph now looks certain to end in bitterness and resentment.

Following the £100million buy-out of Brawn by Mercedes-Benz, and barring any change of heart, Button is expected to confirm that he has concluded a three-year deal worth a minimum of £18m with McLaren and will join Lewis Hamilton in a British superteam.

It is understood Button and McLaren met for further talks last night.

Yet even before the deal is confirmed, accusations have already started flying over why Button and team principal Ross Brawn could not reach their own agreement to maintain what had appeared to be the perfect set-up.

Having masterminded the rescue of Honda after their Japanese paymasters suddenly pulled the plug last December, Brawn exploited his own technical genius and Button's talent behind the steering wheel to win both the 2009 drivers' and constructors' championship.

However, sources in Button's camp are now insisting the 29-year-old has been squeezed out by Mercedes' determination to form their own German superteam around Nico Rosberg, son of former world champion Keke Rosberg, and Nick Heidfeld. And members of the management at Brawn are bristling over claims that they offered Button only a “derisory” rise on his current retainer of around £3m.

Instead, the word coming out of Brawn's headquarters at Brackley in Oxfordshire is that Button's initial demand for £8m was met in principle, only for the champion to come back for more once the Mercedes money arrived on the scene.

Brawn chief executive Nick Fry insisted that Button's financial status was never going to be improved by Mercedes. He said: “I'm sorry to say that it's not going to change anything in that respect.

“The reason Mercedes wanted to buy into our team was that we run it in a conservative way financially. In these tough times it doesn't matter whether you're Mercedes-Benz or anyone else, you have to tighten your belt.”

Refusing to concede that Button is already lost to McLaren, Fry went on: “I hope Jenson will be with us next season. We've worked together for a good few years now, we succeeded in winning the world championship together and we want Jenson to be with us.

“But we have to recognise that Formula One is not divorced from the rest of the world. We work within a budget and if we spend the money in one area we can't spend it in another.

“The reason we survived as a team is that we've operated in a sensible way, we've operated within our means. As chief executive, that's my job and we're going to continue to do the same.”

It is believed that Button has been offered a basic £6m-a-year at McLaren — whose state-of-the-art Woking base he visited last Friday — with the opportunity to bank bonuses that would take his final pay closer to the £10m earned by Hamilton.

Dr Dieter Zetsche, chairman of Daimler and head of Mercedes-Benz Cars, made it clear that Brawn, who masterminded seven drivers' titles for Michael Schumacher as technical director at Benetton and Ferrari before guiding Button to his first title, was the key prize in the takeover.

He said: “It will be a true Mercedes-Benz factory team. As important as that, of course, is that Ross Brawn will continue as team principal.”

He refused to be drawn on who would be driving their cars next season but denied there was a desire to have two Germans in the team. He said: “We would like the best drivers. We wouldn't be opposed if one of them was German but that is not a prerequisite which would be given to the team.”

Germany's Timo Glock, who had been searching for a new team after Toyota quit Formula One earlier this month, has joined Manor Grand Prix.