A British artist claims that a £1m Banksy sculpture that is the centrepiece of a contemporary art auction this week was stolen from him and is being sold illegally.

The Drinker is a subversive nod to Rodin’s The Thinker, the famous statue of a man lost in thought with his chin resting on his hand. Banksy’s sculpture has a similar posture, but the man seems collapsed in a drunken slump, with a traffic cone on his head. The piece was left in a small square off Shaftesbury Avenue in central London in 2004, placed there without planning permission, like almost all Banksy’s public work.

Artist Andy Link, who also goes by the moniker “Art Kieda”, “kidnapped” the piece from its plinth, registered his “find” with police, and contacted Banksy for a ransom. The artist offered “£2 towards a can of petrol” to set the piece on fire; Link kept it in his garden.

Three years later the sculpture – more than 6ft high and very heavy – was taken from Link’s garden while he was away. He went to the police to report the theft.

The statue reappeared this autumn in the Sotheby’s auction catalogue for the 19 November Contemporary Curated sale, with an estimated sale price of £750,000 to £1m, the most expensive item in the sale.

Sotheby’s said it was satisfied the seller had a legal right to put the piece up for auction. It said: “We consulted both the Metropolitan Police and the Art Loss Register.”

Sotheby’s sale notes say the work was “retrieved” – suggesting it was taken from Link by Banksy or his associates. “The work was mysteriously retrieved from Art Kieda’s lock-up in an anonymous heist which left AK47 [Link] with nothing but the abandoned traffic cone from atop The Drinker’s head,” the catalogue said.

Banksy items are usually only sold as authentic if they carry a certificate of authenticity from “Pest Control”, which handles enquiries for the anonymous artist. Representatives for Banksy declined to comment.

Link said that, as the statue had been abandoned on the street, he had registered it with police, and Banksy had not asked for it back, his ownership should be clear. “I did the right thing, and reported it to the police,” he said, detailing the documents and case numbers he has kept over more than a decade. “I do not understand how Sothebys can sell this when I have such proof.”

But he said he could not afford to challenge the sale. “Lawyers are asking from £18,000 up just to take the case on, and I’m a struggling artist, just a working-class bloke. The police should be looking into this,” he said.

The police said: “The Met does not have an active criminal investigation into this matter.”