Stewart believes Mosley's position has become untenable

Three-time Formula One world champion Sir Jackie Stewart says he thinks it is "impossible" Max Mosley can survive as head of world motorsport.

Mosley is under pressure to quit after a newspaper claimed he took part in a "Nazi-style orgy". He denies his actions had any Nazi connotations.

Stewart told the BBC that the big companies which back F1 want Mosley out on both commercial and moral grounds.

"He's gone beyond anything they would tolerate," Stewart told Radio 5 Live.

Stewart, who has clashed with Mosley over many issues in the past, said the sport's big backers had met at the Spanish Grand Prix to discuss the issue.

He said Mosley's behaviour would have contravened the companies' "corporate moral guidelines" and that motor clubs around the world, which also come under the auspices of the FIA, would not approve either.

"Therefore it's very difficult to see how he could stay under these circumstances," added Stewart.

"I think it's going to be very difficult commercially for the companies involved in Formula One to carry that and the motor clubs to carry it. I think that's quite serious."

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On Sunday it emerged that Formula One supremo Bernie Ecclestone, a long-time associate of Mosley, had invited F1 team bosses to sign a letter calling for Mosley to stand down and said he would add his name if they all signed it.

Seven teams agreed, but three did not - Ferrari, Toro Rosso and Williams.

Mosley has called an extraordinary meeting of FIA members for 3 June, where he will face a vote of confidence.

He is also taking legal action against the News of the World, which published the allegations, and is seeking "unlimited damages".