PARIS (REUTERS) - Mercedes accused Formula One's governing body of double standards on Thursday at a tribunal that could impose stiff sanctions on their team for allegedly breaking the rules with a "secret" tyre test.

The team of 2008 world champion Lewis Hamilton - preparing for his home British grand Prix next week - and Germany's Nico Rosberg - face anything from a reprimand to exclusion from the championship if found guilty.

Lawyer Paul Harris, representing Mercedes, suggested the International Automobile Federation (FIA) had treated his team in a very different way to Ferrari, who face no action despite both having tested with tyre supplier Pirelli this year.

Mercedes are charged with breaking the rules by using their current car at a 1,000 km tyre test in Barcelona with Pirelli last month and gaining an unfair advantage from it, an accusation they deny.

Ferrari, who have tested twice previously with Pirell1 including in April just before they won the Spanish Grand Prix at the same circuit, have not been summoned to the tribunal because they used a 2011 car.

"The key differences in treatment are plain," said Harris, criticising a sporting body run by former Ferrari team boss Jean Todt.

"Ferrari were allowed to rely on a verbal confirmation from Pirelli that authorisation had been achieved but apparently we are condemned for this."