The group are determined to have their demands met

Led by car-makers Renault, BMW, Honda, Daimler-Chrysler and Toyota, the Grand Prix Manufacturers' Association is demanding a greater share of F1 income.

The GPMA has been involved in "constructive" talks with motorsport's governing body the FIA over the summer.

But it has announced the continuation of plans to launch a 2008 rival series.

The current uncertainty leaves them with no option other than to progress preparatory work for the new series A GPMA statement

The GPMA, together with the seven teams associated with them, met FIA president Max Mosley twice over the summer, with all sides declaring the talks to be positive.

However, the GPMA said it is ready to start work on carrying out its threat of the breakaway series when F1's ruling Concorde Agreement expires in 2008.

A GPMA statement said: "Whilst the group remains open and willing to discuss with the current commercial rights holder, Bernie Ecclestone, 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.

"Although the team principals and manufacturers agreed that some progress was made in the recent meetings, they considered it was not sufficient to delay the preparations for the new series."

In Brazil last weekend, Renault motorsport president Patrick Faure outlined the group's determination to have their demands met.

He said: "I think we will reasonably hold firm because our target has been the same since the beginning.

"That is to say that we must give more money to the teams who are really organising the show - and on this we will not compromise.

"We want more money, not for us, the manufacturers, but for all the teams."