Footballer David Beckham and his Spice Girl wife Victoria invented a story of a snatch attempt on their son to get Beckham off a speeding charge, an unauthorised biography claims.

In his book, Posh and Becks, Andrew Morton suggests the couple manipulated the media to exaggerate fears for their safety in public.

David Beckham was banned from driving for eight months in December 1999 after he was caught driving his Ferrari at 76mph on a 50mph road in Stockport, Cheshire. The Manchester United midfielder appealed against the sentence claiming he was pursued by a paparazzi photographer for 10 miles and feared for his safety - although the photographer's car was never traced.

In a five-hour appeal hearing at Manchester crown court, Beckham, 25, told Judge Barry Woodward that a snatch attempt on their one-year-old son at Harrods the same week illustrated his fears. He said the couple were Christmas shopping with Brooklyn when a crazed fan lunged at their son demanding a photograph of the family.

The judge - who called Beckham an "honest and truthful witness" - handed back his licence but upheld the speeding conviction and an £800 fine.

But Morton's book casts doubts over the Harrods incident.

"Strangely, the incident was not captured on film either by the CCTV cameras outside Harrods or by the dozen or so photographers within inches of their Mercedes. A housewife quoted as a witness has proved untraceable," Morton writes.

A photographer who was present adds: "David Beckham had a court case at the time. He used the incident, spin-doctoring to get him off. There was no manic fan."

Morton quotes the Harrods media relations officer, Michael Mann, as saying: "No one saw it, not the doormen and not the photographers. In my opinion it may not have happened and was possibly for the papers."

A spokeswoman for the Beckhams said the couple strongly refuted suggestions that the Brooklyn incident was fabricated and the couple were disappointed that the allegations had been given credence.

"The book does not actually claim that the incident did not happen but simply reports that some people do not believe it. It is a poor attempt to make the book look controversial to generate sales," she said.

Morton's 224-page book, which is serialised in Hello! magazine next week and published next month, was the subject of a high court action in August.

The Beckhams sought an injunction to prevent publication objecting to disclosures about their private life from former bodyguard, Mark Niblett. They settled the claim after 200 words were deleted from the manuscript, rather than the 2,500 they had wanted removed. The couple were left with a £100,000 legal bill.