Formula One’s governing body, the FIA, has declared the controversial double-decker diffuser designs on the Brawn GP, Toyota and Williams cars as legal.

After lengthy deliberations overnight, the judges at the International Court of Appeal hearing in Paris rejected protests against the design from Ferrari, Red Bull Racing, and Renault.

The FIA said in a statement: “The FIA International Court of Appeal has decided to deny the appeals submitted against decisions numbered 16 to 24 taken by the Panel of the Stewards on 26 March at the 2009 Grand Prix of Australia and counting towards the 2009 FIA Formula One World Championship.”

“Based on the arguments heard and evidence before it, the Court has concluded that the Stewards were correct to find that the cars in question comply with the applicable regulations.”

The ruling has huge implications on the outcome of the 2009 Formula One World Championship with those teams running regular diffusers now forced to play catch-up.

The decision is good news for Jenson Button who won the opening two races of the season for Brawn GP and finds himself in a strong position to challenge for the title. The British driver could have been stripped of his points had the judges ruled in favor of the protesting teams.

“We are pleased with the decision reached by the International Court of Appeal today,” said team principal Ross Brawn. “We respect the right of our competitors to query any design or concept used on our cars through the channels available to them.”

“The FIA Technical Department, the Stewards at the Australian and Malaysian Grands Prix and now five judges at the International Court of Appeal have confirmed our belief that our cars have always strictly complied with the 2009 Technical Regulations.

“The decision of the International Court of Appeal brings this matter to its conclusion and we look forward to continuing on the track the challenge of what has been a very exciting start to the 2009 FIA Formula One World Championship.”