The statue of the river god Ilissos has been lent to the State Hermitage Museum in St Petersburg for an exhibition until mid-January.
It is the first time one of the 2,500-year-old Marbles has been removed from the museum – except in wartime – since they were presented to the London institution almost 200 years ago after being removed from the Parthenon temple on the Acropolis by Lord Elgin.
Greece maintains they were taken illegally during the country’s Turkish occupation and should be returned for display in Athens, which the British Museum and the Government reject.
The British Museum’s director indicated that he would be willing to consider a similar loan of a statue to Greece – but only if the authorities there promised to return it to London.
Neil MacGregor said the museum’s trustees would “consider any request from anyone who is prepared to return the object”.
But the chairman of the Marbles Reunited campaign, Liberal Democrat MP Andrew George, said the trustees were wrong to snub the Greek request for the return of the sculptures and to lend them instead “to a country which has backed rebels who kill British citizens”.
In October a team of London lawyers, including Amal Clooney, were involved in talks with the Greek government about a potential legal bid for the works.
Her husband, actor George Clooney, has said it was “probably a good idea” for them to be returned.