A war of words to match the sharpest of Shakespeare’s own satires has broken out between two eminent scholars over a recently-discovered portrait said to be of the Bard.

A previously unknown painting unveiled last month was said to be the only surviving portrait of Shakespeare painted during his lifetime.

And those claims were given vital backing from influential supporter Professor Stanley Wells, chairman of the Shakespeare Birthplace Trust and general editor of the Oxford Shakespeare. But now, in the opposing academic corner, comes Sir Roy Strong, a former director of the Victoria and Albert Museum and the National Portrait Gallery, who has branded claims that the portrait is of Shakespeare as “codswallop”.

Sir Roy told the Observer: “I don’t know why Stanley Wells has gone off on this fantasy journey. It is codswallop, isn’t it?”

The portrait by an unknown artist has been in the same Anglo-Irish family for 300 years and never previously shown in public. It came to light after its present owner, picture restorer Alec Cobbe, noticed its similarity to a painting from the Folger Shakespeare Library in Washington DC which was on loan to the National Portrait Gallery exhibition, Searching for Shakespeare, in 2006.

Following three years of research, it is now claimed that the Cobbe portrait was painted from life in about 1610, when Shakespeare was 46 and had six years to live. At least four copies exist, including the Folger portrait. Sir Roy added: “The Cobbe is just one of a number of around 15 portraits from that era of middle-aged men that are effectively anonymous.”

Prof Wells, speaking to the Birmingham Post last month, said he was “very sceptical” that the Cobbe portrait was of Shakespeare but had gradually become convinced. “I’m 90 per cent persuaded. The only thing that would be totally convincing would be if we had a receipt that said ‘paid to someone, 40 shillings for painting a portrait of Shakespeare’.”