La Bella Principessa not a da Vinci, it's Sally from the Co-op, claims art forger

Forger Shaun Greenhalgh and the Leonardo da Vinci drawing he claims he did in 1978.

A Leonardo da Vinci drawing believed to be worth $230 million is actually a picture of "Sally from the Co-op" in Bolton, one of Britain's most notorious art forgers has claimed.

The La Bella Principessa purports to be a portrait of a young woman possibly from the court of Ludovico Sforza, the duke of Milan, in the 1490s.

But Shaun Greenhalgh claims he drew the picture in 1978 based on a "bossy" shop assistant he worked with at his local Co-op store in the north west town.

He claims he used an old council document dating back more than 400 years as a canvas and specially created pigments to con the art world.

He makes the revelations in a new book but experts have cast doubt on his claims over what is already a very controversial drawing.

Mr Greenhalgh, who was jailed for four year and eight months for forgery in 2007, said: "I drew this picture in 1978 when I worked at the Co-op.

"The 'sitter' was based on a girl called Sally who worked on the checkouts," he writes. "Despite her humble position, she was a bossy little bugger and very self-important."

The forger said he used a council document dated from 1587 as a canvas and a Victorian school desk lid as the backing.

However, laboratory testing of the artwork over the last two years had concluded it is at least 250 years old.

The "La Bella Principessa" is said to be worth $230 million.

Martin Kemp, an emeritus professor at Oxford and an expert on da Vinci, is certain the girl is Sforza's illegitimate daughter Bianca, whose husband was Leonardo's patron.

And a previous seller said her husband had the painting before she married him in 1955.

The picture has been mired on controversy since it was listed for auction at Christie's in New York in 1998.

The then owner Jeanne Marchig told the auction house she thought it came from 15th century Italy, but was told it was by a 19th-century German and it sold for the equivalent of £14,500 at today's rates.

It has since been argued it is a da Vinci and could be worth more than £100 million.