By the time of Joyce Hatto’s death last June, her recordings had made her one of the world’s most admired pianists.

Her obituary in The Times related the extraordinary story of how, after she had cancer diagnosed in 1970, Hatto retreated from the concert platform to a studio set up by her husband “to bequeath to the discerning pianophile one of the most remarkable recording legacies of the 20th century”.

The Guardian praised a discography “that in quantity, musical range and consistent quality has been equalled by few pianists in history”. The Independent called her “a national treasure”.

Music lovers marvelled at the story of a hitherto obscure performer who, crippled by illness, found the strength and inspiration to produce world-class interpretations of some of the most complex works well into her seventies.

Now it appears that Hatto’s prolific output concealed a troubling secret. Research by the critics at Gramophone magazine suggests that several of “her” recordings are those of other, better-known virtuosi.

Analysis of 4 of her 119 recordings has shown them to be identical to discs by László Simon, Yefim Bronfman, Minoru Nojima and Carlo Grante.

James Inverne, the editor of Gramophone, said yesterday: “This is a scandal. Sadly it seems that some of these recordings do not feature, as we thought, an unknown piano genius but rather other piano geniuses who are very well known.”

Hatto was born in North London on September 5, 1928, the daughter of an antique dealer who adored music and above all Rachmaninov, who, she said, seemed to be “almost a relative, like some sort of uncle”.

She honed her technique through hours of practice during the Blitz, hiding under the family piano during bombing raids. Sir Granville Bantock declared: “This child is a born performer”; the late Sir Michael Tippett urged her to devote her life to Bach. But she was put off musical institutions when a tutor at the Royal Academy informed her: “It’s really more important for a young girl like you to be able to cook a good roast dinner and not bother with all this.”

Undeterred, she became a concert pianist in the 1950s and 1960s and toured Russia, Poland and Scandinavia.

The diagnosis in 1970 changed her life. She stopped performing in 1976 after a critic noted savagely that it was “impolite to look ill”.

Instead, she retreated to the Hertfordshire home she shared with her husband, William Barrington-Coupe, the A&R manager for the budget label Saga. He gently encouraged her to record. Gramophone was the first publication to champion this late career body of work early in 2006 and Hatto’s recordings rapidly became a cult.

Her “miraculous performances”, all released by Barrington-Coupe on the tiny label Concert Artist, were difficult to get hold of and quickly became collectable. They covered a formidable range, from Haydn, Mozart, Beethoven, Brahms, Liszt, Schubert and Rachmaninov to Dukas, Godowsky, Scarlatti, Bliss, Rawsthorne and Bax.

They also provoked a wave of conspiracy theories on the internet. How, the doubters whispered, could one frail woman who had retired from the concert stage more than 30 years ago master such a repertoire?

Gramophone challenged readers to prove that the recordings were fake or let the matter rest as a mark of respect for an ailing woman. Nobody came forward and Hatto died on June 30, last year.

Then, this week, a critic at Gramophone decided to listen to a Hatto Liszt CD. When he put the disc into his computer it automatically identified it as a recording by the pianist Lás-zló Simon. Intrigued, the critic checked his Hatto disc against the actual Simon recording, finding that they sounded exactly the same.

When he tried a Hatto Rachmaninov recording, he found that it was listed as a performance by Yefim Bronfman, conducted by Esa-Pekka Salonen.

Andrew Rose, an audio expert with Pristine Audio, then analysed the recordings and found that they tallied exactly with performances by Simon, Bronfman and Nojima. Closer examination of a Hatto performance of Godowsky revealed that it had been manipulated — stretched by more than 15 per cent — to alter the tone, but was identifiably by the pianist Carlo Grante.

Mr Inverne said that it was not yet clear how many, if any, of Hatto’s late recordings were her own work. “So far we have checked four different sets of music. People are now coming to us thick and fast with new allegations.”

Mr Barrington-Coupe was unavailable for comment last night.

Faking it?

Hans Van Meegeren was jailed in 1946 for collaborating with the Nazis after it emerged he had sold a Vermeer to Hermann Goering. He revealed that he had forged it, and proved the point by painting a new “Vermeer”, embarrassing art experts

Elmyr de Hory conned people with his forgeries of Modigliani, Matisse and Picasso in the 1950s and 1960s. He was the subject of the Orson Welles documentary F for Fake

George Harrison was ordered to pay ABKCO Music $587,000 (£400,000) in a plagiarism case, after it emerged that his 1971 hit My Sweet Lord bore a striking resemblance to He’s So Fine by the Chiffons.

Glenn Brown’s version of a sci-fi novel’s cover, shown as part of his 2000 Turner Prize display, made an illustrator claim for breach of copyright

Jean de Sperati, a master forger, had more than 1,500 stamps auctioned at Sotherby’s earlier this year

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