For many years, authors, naval historians and tour guides have believed that Lord Nelson went into battle at Trafalgar accompanied by a fearless pet cat called Tiddles. An appearance on breakfast television earlier this month has led to the shock discovery that Nelson's cat was, in fact, a hoax perpetrated 15 years ago by a National Trust employee called Guy Evans.

Stephen Fry uncovered the scam after mentioning Tiddles during a BBC interview to plug the DVD of his quiz show QI. A few days later, he received a letter from Evans's widow, Anna.

'I ought to tell the world that Tiddles is a myth,' it read. 'He first appeared in a letter written by my husband to The Spectator in 1990. He followed it up in an article in the Nelson Society Journal, with very convincing and entirely fictional footnotes.

'From there, Tiddles snowballed to become part of popular folklore and has featured in books, magazines and academic journals.'

Fry's producer, John Lloyd, says this has surprised even tour guides on HMS Victory. 'We research questions exhaustively at QI, and we have never come across something like this before,' he tells me.