Five Formula One carmakers and seven of the 10 teams have signed a 'binding agreement' to stand firm in the battle with Bernie Ecclestone over the sport's commercial future.

The manufacturers are threatening to launch their own series from 2008 if they are not given far more of the revenues and issued a statement after meeting near Munich.

They said preparations for their series had moved forward, with consultants International Sports and Entertainment AG (iSe) instructed to advance negotiations with broadcasters, circuit owners and sponsors.

"The five manufacturers and the teams entered into a binding agreement to race together only in a series which satisfies the fundamental principles of a clear and equitable world championship," the statement said.

"All teams not party to this agreement are encouraged to participate in a constructive process to form the premier motorsport series.

"Whilst the group remains open and willing to discuss with the commercial rights holder and the FIA on the future of grand prix motor racing beyond 2007, the current uncertainty leaves them with no option other than to progress preparatory work for the new series."

Ferrari, the current champions, Jordan and Red Bull have already agreed with the governing International Automobile Federation (FIA) and Ecclestone's Formula One Management to extend the existing commercial agreement to 2012.

The current agreement expires at the end of 2007. The carmakers are BMW, DaimlerChrysler's Mercedes, Renault, Toyota and Honda.

Minardi, due to be taken over by Red Bull on November 1 after owner Paul Stoddart was bought out, attended the meeting and the Australian entrepreneur also signed the declaration.

The team are expected to leave the group of seven teams once they come under Red Bull's control.

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