Formula One will not be improved by rule changes allowing teams to use so-called 'customer cars' in 2008, according to BMW-Sauber boss Mario Theissen.

At present, teams must design and build their own chassis but those rules are being relaxed next year to try to cut costs and allow the smaller, independent outfits to become more competitive.

British-based Prodrive, due to become the 12th team in 2008, have already said they intend to do a deal with one of the major manufacturer teams.

There are also concerns that Honda-backed Super Aguri and Red Bull's Toro Rosso will try and pre-empt matters this year with cars bearing a strong resemblance to last year's Honda and the latest Red Bull respectively.

"There certainly is a debate about the legality of using cars not designed by their own team in 2007," Theissen told reporters after the launch of BMW's new car in Valencia on Tuesday.

"To me, it's not so much of an issue ... my concern is not about 2007 but about the general rule of chassis sale in future," he said.

"In my view it will change the shape of Formula One.

"I expect a new breed of so-called independent teams to come up -- teams who see the whole thing as a business case and team up with a strong manufacturer team in order to get the chassis and entire car for just a little money," said Theissen.

In exchange for that, he said they would be expected to support the manufacturer team on the racetrack.

Theissen said that could lead to Formula One having effectively only six four-car teams on the starting grid.

"I'm not sure if this is really beneficial to Formula One," he declared.

"If you imagine when the championship comes into the final phase, and only one driver in the team has a chance to become champion, a team could use three cars to support one driver.

"I think what we have now with 11 or 12 really independent teams is much better for the sport."