Mercedes will turn the tables on the FIA at Thursday's hearing in Paris by producing written evidence that they had permission to test Pirelli's tyres.

Both Mercedes and the Italian tyre firm will be in the dock after the Formula One's governing body decided they had a case to answer following their three-day, 1,000km test in Barcelona after last month's Spanish Grand Prix. The test enraged the other teams, particularly Red Bull. Contrary to FIA regulations, Mercedes used their current 2013 car rather than one at least two years old, as favoured by Ferrari in another testing session. But Mercedes are ready to play their trump card, in the form of an FIA email – allegedly from their race director and safety delegate, Charlie Whiting – granting them permission to test.

It is difficult to believe that Ross Brawn, the Mercedes team principal who is the most successful team leader of his generation, would have gone along with the test unless he felt sure of his ground. He said in Montreal last week: "We wouldn't have done the Pirelli test unless we believed we could do the Pirelli test and I believe when we get to tribunal you'll have your answers."

Brawn, taking exception to accusations that the test was secret, added: "There's been an unfortunate branding of a 'secret' test – it was a private test, it wasn't a secret test. If anyone believes you can go to Barcelona and do three days of testing, or 1,000km of testing, and not have anyone become aware of it is naive. So it was a private test, not a secret test."

If Mercedes or Pirelli are found guilty they are likely to go the FIA's international court of appeal in an attempt to get the verdict overturned. There is even an outside chance that Mercedes could walk away from the sport if they feel they have been dealt with harshly, although that is unlikely given their recent level of investment.

If they did exit Formula One, which they have already considered in recent years, it would leave a massive hole in grand prix racing. Next year McLaren, Force India and Williams are all scheduled to run with Mercedes engines.

Pirelli are also likely to consider their future in F1 if the hearing goes against them. They are already hampered by a lack of in-season testing, and for some time their appeals for help developing the tyres have gone unheeded by the teams.

Meanwhile, José Froilán González, the first man to win a world championship F1 race for Ferrari and nicknamed the Pampas Bull, has died at the age of 90. The Argentinian followed his countryman Juan Manuel Fangio to European racing in 1950 was hired by Ferrari a year later and became their first F1 winner as he defeated Fangio's Alfa Romeo to win the British Grand Prix at Silverstone.