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Swiss dealer Jean-David Cahn was appointed by the Swiss canton of Basel-Stadt to sell the objects and he offered them at the Regent’s Park fair earlier this month.

However, forensic archaeologist Christos Tsirogiannis, a specialist in trafficking of illicit antiquities, produced evidence that in fact the objects were looted and should not be for sale.

On October 26 Greece’s culture ministry issued a statement to say it is seeking the repatriation of the vases.

Tsirogiannis told ATG: “The authorities in Basel and the dealer Jean-David Cahn (and anyone involved in any case of an antiquity with an incomplete and not documented history), should refer to all state authorities who may have a possible claim and access to the archives before they offer any antiquity for sale.”

Tsirogiannis also said he believed dealers should present the full provenance they have for an object on their stand, rather than only give the information to those who enquire. He added: “Both the Canton of Basel and Cahn knew that the antiquities were part of the Becchina stock, but this crucial information was [not on show to] the public.”

Gerhard Kuhn, head of Basel’s bankruptcy office, told ATG: “We sought legal opinion and the public prosecution department said they could be sold. If there is new evidence, that we did not have access to before, then the situation will be of course be reviewed.”

The vessels, an oil vase called a lekythos and a water vase called a loutrophoros, came from the former stock of disgraced art dealer Gianfranco Becchina. Over the past decade the Italian police investigated more than 5000 objects from Becchina before releasing more than 1000 to the Swiss authorities, who planned to sell the goods to raise revenue owed to the state by Becchina.

“This case illustrates the difficulties that all in the trade face in due diligence

A Frieze spokesperson said: “The Canton of Basel had cleared these works through the Italian carabinieri … Mr Cahn is a respected dealer who has a history of participation at reputable art fairs globally, all of which are vetted by the Art Loss Register (ALR).”

ALR director of recoveries and general counsel James Ratcliffe told ATG an ALR certificate was issued to Cahn after Basel authorities confirmed they could sell with good title.

He added: “It seems now as though either the Swiss or Italian authorities missed… indications of looting.

“It is a significant problem if the authorities cannot be trusted to do their research… I think this case illustrates the difficulties that all in the trade face when trying to do their due diligence if potential claimants are not cooperative.”

Becchina and another dealer Giacomo Medici were both investigated for trafficking stolen antiquities. An archive of their former stock is available to academics only and is where Tsirogiannis sources information.

The ALR, auction houses and dealers have continued to call for access to these archives.