Just four days after being vindicated as an original author by the High Court in London, the multi-millionaire writer of The Da Vinci Code has been accused of another allegation of plagiarism.

This time Dan Brown has been accused of pinching a Russian art researcher's theory that the Mona Lisa harbours a secret message and is, in fact, an amalgam of the faces of Jesus Christ and the Virgin Mary.

Mikhail Anikin, a senior researcher in the Department of the History of Western European Art at the Hermitage museum in St Petersburg, has claimed that he shared his idea with a colleague in Texas who asked if he could pass on the idea to "detective book author" he knew.

Mr Anikin said today that Brown was the "detective book author" in question and that he was entitled to an apology and compensation for "everything Dan Brown has got from this plagiarism".

"Otherwise, I intend to take legal action in the next few days," he told Agence France Presse.

The Da Vinci Code, the book that contains what Mr Anikin believes is his stolen idea, has sold 40 million copies, including 4 million in the UK, and made Brown £45 million in a single year. It has spawned a genre of copycat bestsellers, a boom in visits to the Louvre and is also the subject of a Hollywood movie starring Tom Hanks due to hit the big screen next month.

According to Mr Anikin, Brown "plagiarised my idea that Leonardo Da Vinci was not only a painter but also a theologian and that his Mona Lisa was not a portrait but an allegory representing the Christian church".

Mr Anikin said he had written a book called “Leonardo Da Vinci: Theology In Paint” in 2000, in which he argued that the artist’s painting, the Mona Lisa, was an allegory representing the Christian church.

"The Mona Lisa consists of two images," said Mr Anikin. "Those of Christ and the Virgin Mary, and represents the Da Vinci code."

In 1998, Mr Anikin said he shared his idea with colleagues at a museum in Houston, Texas, and that one man, an art expert called William Sten, asked if he could tell a friend of his who was writing a book. "I gave permission, but asked that this author indicate in his book that the idea had been mine," said Mr Anikin.

The plot of The Da Vinci Code centres on the idea that after the resurrection, Jesus married Mary Magdalene and sired a line of kings determined to rule Europe. A secret society, known as the Priory of Sion, was spawned to protect the secret and protect the line.

Under the "true facts" section of Brown's website, the author says the work of Leonardo da Vinci, including the Mona Lisa, are central to unravelling the code.

"Most scholars agree that even Da Vinci's most famous pieces — works like The Mona Lisa, The Last Supper, and Madonna of the Rocks — contain startling anomalies that all seem to be whispering the same cryptic message," the website says.

Brown did not immediately respond to the latest allegations. At the end of last week's trial, Richard Leigh and Michael Baigent - the authors who claimed Brown built his best-seller on the central thesis of their 1980s work Holy Blood, Holy Grail were landed with a £2 million legal bill.

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