Frank Williams insists that he is fully prepared to challenge the legality of both the Toro Rosso and Super Aguri, should they go ahead and use cars derived from the Red Bull (RB3) and Honda (RA106). The Englishman has revealed that he is about to launch arbitration proceedings at the International Chamber of Commerce in Lausanne.

There is growing unease between many of the teams regarding the issue of 'customer cars', even if Williams and Spyker are the only teams currently discussing the matter in public.

In much the same way as many team principals kept their heads down when (Minardi boss) Paul Stoddart was at loggerheads with the FIA regarding the possibility of a breakaway F1 series, so Williams and Spyker appear to be the only teams willing to voice their concern publicly via-a-vis customer cars.

A recent attempt by Bernie Ecclestone to placate the teams failed, leading to fears that the season opener in Melbourne will be marred by legal challenges and protests.

"I am adamantly opposed to chassis sharing," Frank Williams tells Alan Henry of The Guardian, "and we at Williams do not believe it is legal under the current rules. We are what you might call a traditionalist racing team which believes that we are out there competing for two world championships, one for the best driver in the world and one for the constructor who builds the best car in the world. As far as I'm concerned it is absolutely in the regulations in black and white that every team must make its own chassis."

Both Toro Rosso and Super Aguri are circumventing the official rules regarding customer cars by having the cars built by a third party, a loophole which, according to FIA President Max Mosley, is perfectly legal.

The other teams are watching the situation with interest, though other than Spyker and Williams, only (BMW boss) Mario Theissen has spoken out over the issue, concerned that customer cars will lead to 'four car teams'.

Williams also expressed his unease at Prodrive's F1 entry in 2008, the British team intending to use a customer chassis and engine, having secured the so-called 'twelfth spot'.

Though the FIA accepted numerous bids for the twelfth team many F1 insiders felt the decision was a foregone conclusion, and even though several of the teams bidding for the slot on the 2008 grid already had virtually everything in place, including the necessary structure to build their own chassis, it was Prodrive that got the nod.

"In the presently issued rules for 2008, customer cars are not yet a done deal," warned Williams.