Fernando Alonso’s future at McLaren Mercedes is in doubt after allegations that he threatened to tell the FIA, the governing body of motor sport, about Ferrari secrets on his computer unless he was confirmed as the team’s No 1 driver.

The disclosures increase the likelihood that the Spaniard will not drive for the Woking-based team next season and will possibly join Renault or even take a year’s sabbatical. There were even suggestions that he may not survive the remainder of this season, which would effectively present the world championship to Lewis Hamilton, his rookie team-mate.

Alonso is alleged to have made his threat during a row with Ron Dennis, the McLaren team principal, on the morning of the Hungarian Grand Prix on August 5. It came as Alonso tried to force Dennis to give him preferential treatment over Hamilton, the championship leader, or let him leave McLaren at the end of the season.

The details of the row, which spread like wildfire in the paddock in Spa, where the Belgian Grand Prix is being staged this weekend, leaked from McLaren after it was reported on an internet site that it had been Dennis who informed the FIA of new evidence linking his team to the Ferrari spying scandal. That revelation was followed by the publication by the FIA yesterday of the details of its judgment against McLaren on Thursday that resulted in a fine of £50 million and the team being thrown out of this year’s constructors’ championship.

Bernie Ecclestone, the ringmaster of Formula One, said that he campaigned for McLaren to be fined by the FIA, but admitted that the Woking-based team came close to exclusion from the championship for two years. “It came very close to McLaren being thrown out, it really was a genuine possibility,” Ecclestone said.