A portrait of Shakespeare that has been in the collection of the Royal Shakespeare Company in Stratford-upon-Avon since 1892 has secretly been replaced by a 19th-century fake during the past decade, a German scholar claims.

Hildegard Hammerschmidt-Hummel said that the famous portrait, The Flower, was not the original that she examined between 1995 and 2005 and which was among the very few reliable likenesses of the playwright.

Professor Hammerschmidt-Hummel said yesterday that the original had been substituted by a copy. In 2005 it was sent to the laboratories of the National Portrait Gallery and dismissed as a 19th century forgery after it was found to contain chrome yellow, a colour that was commercially available only from 1814 onwards.

“Where is the priceless 400-year-old original Flower portrait?” asked the professor, who lectures in English literature at the University of Mainz.

She said that she was basing her conclusions on tests that she carried out on what she says was the original – which she she last saw in 1996 – and on the version that she claims is a copy, which she saw in January.

She indicated that evidence found in X-rays and photographs, and the support of Viennese experts in the Old Masters and forensic science, gave weight to the theory. But the RSC and NPG have said that any perceived differences are caused by lighting conditions and different equipment.

Professor Hammerschmidt-Hum-mel said that she became suspicious after her German publishers contacted the RSC and requested a transparency of the portrait for reproduction in her forthcoming book. She said that they received a picture that she claimed was “strikingly different” from the one supplied by the company in 1996.

She commissioned scientific tests from Reinhardt Altmann, an expert at the German Federal Bureau of Criminal Investigation.She said: “Altmann concluded that the picture provided in 2002 must be a copy. Professor Wolf-gang Speyer, of the University of Salz-burg and an expert on Old Masters, confirmed the differences between the two pictures.”

She said that the wood of the painting’s panel in Stratford was in sharp contrast to that of the original. Professor Hammerschmidt-Hummel said: “It had already been described in these terms by British experts at the end of the 19th and the beginning of the 20th centuries, among them the directors of the National Portrait Gallery.”

The edges of the portrait examined in January were “solid, showing no signs of wormwood damage . . . [and] the peripheral areas, which in the original painting are brittle and have been broken or chipped away in places, exhibit no such damage in the portrait inspected in the RSC depository”.

She noted that the original had a deep crack, whereas the alleged copy had “an imitated crack”. David Howells, the curator of the RSC collection, said that the crack “doesn’t appear to be identical. It’s not there as she remembers seeing it, but that was over ten years ago.”

An X-ray examination in 1966 by the Courtauld Institute of Art revealed that a painting of a Madonna and the Christ child from the late 15th or early 16th century lay beneath the portrait.

Professor Hammerschmidt-Hum-mel said: “In the older X-ray, the outline of the right-hand side of the Madonna’s head runs through Shakespeare’s left eye, close to the nasal side of the pupil. The new X-ray mistakenly has what appears to be the bridge of the Madonna’s nose bisecting Shakespeare’s left eye. The conclusion must be that the Madonna beneath the portrait is a poor imitation and it follows that the portrait is not genuine.”

Both the RSC and the portrait gallery rejected the claims. A spokes-woman for the RSC said that the only time the painting had not been on display under CCTV coverage in the RSC Collection Gallery was when it was in a secure store room. Dr Tarnya Cooper, the portrait gallery’s 16th century curator, said: “The idea that this picture has been substituted for a different portrait between 1996 and 2005 is plainly nonsensical . . . Any perceived differences between photographs are likely to be caused by differences in lighting conditions.”

Stanley Wells, Britain’s foremost Shakespeare scholar, condemned Professor Hammerschmidt-Hummel’s claims as “disgraceful”. He claimed that she was trying to counter the evidence against the painting’s authenticity, following the NPG’s research, and added that many books written on Shakespeare contained “lunatic theories”. He said of Professor Ham-merschmidt-Hummel: “She knows her way round the archives, but she barks continually up the wrong tree. At least she’s not saying Shakespeare didn’t write Shakespeare.”

Chaucer Press will be publishing Professor Hammerschmidt-Hummel’s findings in The Life and Times of William Shakespeare on November 5.

Centuries of forgery, feud and fantasy

— Academics have argued for centuries over the authorship of Shakespeare’s works; the philosopher Francis Bacon, the nobleman Edward de Vere and the playwright Christopher Marlowe are among suggested candidates

— A former physics teacher from Cheshire published a book this year claiming that the works were written by the unknown illegitimate son of Elizabeth I. Robert Nield argued that anagrams in the sonnets show their author to be William Hastings, who he believes was the illegitimate child of Elizabeth and Robert Dudley, the Earl of Leicester

— Lloyd Sullivan, a Canadian, recently produced a portrait dated 1603 and labelled “Shakespeare” which his family had kept under the bed. Analysis showed it was not forged, and was painted in the 17th century, but the identity of the sitter was not proved

— John Payne Collier (1789-1883), an early newspaper reporter, was caught out attempting to forge notes by Shakespeare in a carefully studied 16th-century hand

— The most famous fakery came courtesy of William Henry Ireland, an 18th-century teenage forger whose works became hugely valuable in their own right. Ireland duped the elite with his astonishing “discovery” of a cache of documents. He wrote letters revealing correspondence between Shakespeare and Elizabeth I, and Anne Hathaway (accompanied by a lock of her hair), as well as sanitised versions of Hamlet and King Lear. He was exposed when he unearthed a copy of a previously unknown play. It was so bad that the game was finally up

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