A bitter dispute over a painting bought for £140 five decades ago reaches the High Court today – with some of the world’s most prominent Caravaggio experts lining up to take sides.

Sotheby’s is being sued over claims that it misattributed a work – The Cardsharps – to a follower of Caravaggio rather than the Italian painter himself, costing the seller millions of pounds.

The painting was sold through the auction house in 2006 by a descendant of a Royal Navy surgeon who first acquired it in 1962. Sir Denis Mahon, a British collector, secured the painting for a hammer price of £42,000 – but then declared the work to be an original and valued it at £10m.

In papers filed at the court, the seller, Lancelot Thwaytes, claims that the auction house did not consult enough experts or sufficiently test the painting before the sale.

The painting is nearly identical to another under the same name on display at Kimbell Art Museum in Texas. The paintings show a young, privileged man falling victim to a pair of cheats during a game of cards.

Sotheby’s has robustly countered the claims and said that the version it sold was “clearly inferior” in quality to the original painting in the Texas gallery. In the 2006 sale catalogue, Sotheby’s listed it as being by a “follower of Michelangelo Merisi da Caravaggio”.

“The Kimbell Cardsharps was painted by Caravaggio with the striking virtuosity and realism for which his early works are famous,” according to papers filed by the auction house. “The quality of execution on display in the painting falls far short of the Kimbell original.”

It has cited the British biographer of Caravaggio, Helen Langdon, and other leading scholars including the American art historian Richard Spear to support its defence that the painting was a copy.

It said that it would not have consulted any of the experts cited by Mr Thwaytes as leading Caravaggio scholars and said that its own team was competent to judge that it was a copy.

The experts cited by Mr Thwaytes included Mina Gregori, an author of several books on Caravaggio, who claimed last week to have solved a centuries-old mystery by identifying a previously unknown work in a private collection as a Caravaggio. Other experts Mr Thwaytes claims have backed the painting as a genuine Caravaggio include the director of the Vatican Museums, Antonio Paolucci.

Paintings by Caravaggio, who died aged 38 in 1610, rarely come to auction, and when he died, only 50 were known to exist

Sir Denis Mahon had a reputation for identifying a number of paintings by Caravaggio previously thought lost. They included the Young St John the Baptist, which he reportedly saw hanging in the office of Rome’s mayor and had been considered a copy.

The Baroque expert, a member of Guinness Mahon Irish merchant banking dynasty, died in 2011 and bequeathed 58 of his works valued at tens of millions to British galleries, including the National .