No one's been able to do it yet but a small group of 18 members of the United States Congress wrote British Prime Minister Boris Johnson telling him to have the stolen Parthenon Marbles housed in the British Museum returned to Greece or face consequences that could jeopardize relations with the US.

The group said negotiations “in earnest” should be conducted but Johnson's government said marbles belong to the British now and Greece's New Democracy government said it wouldn't use any veto power as the United Kingdom gets set to leave the European Union by year's end to get them back. 

In 2018, a leaked draft of the EU's negotiation mandate included a stipulation that Britain should “return unlawfully removed cultural objects to their countries of origin,” that the British feared meant the Parthenon Marbles, ruling that out flatly.

The Congressional contingent wrote, 'The Marbles have been the source of controversy among western allies for many decades. Greece has long wanted these Parthenon Marbles back.”

The backers for Greece include both Republicans and Democrats and included the heads of the Foreign Affairs subcommittee covering Europe and the the Oversight and Rules committees, the British newspaper The Daily Mail reported.

They want to see the sculptures returned by 2021 – the 200th anniversary of the modern Greek state's founding but even Prime Minister Kyriakos Mitsotakis hasn't been as aggressive as now the US side, saying once he wanted them loaned back.

The letter adds: “We remain appreciative of your efforts and good will in support of the historic special relationship between the United Kingdom and the United States, and look forward to strengthening that relationship through the accomplishment of matters such as this,” sugarcoating the demand with diplomatic boilerplate.

The Marbles were removed from the Parthenon in Athens by Thomas Bruce, the 7th Earl of Elgin, between 1801-1805, then British Ambassador to the Ottoman Empire which was ruling Greece.

He said he had permission to remove them from the Turks, who didn't own them and their theft, British Museum curator Hartwig Fischer said, was a “creative act,” and that they would never – never – be returned. 

A source told the Daily Telegraph: “These members of Congress are saying thank you to Britain for looking after them. They know that Boris Johnson understands Greek history better than anyone, and both Republicans and Democrats are calling on the prime minister to do the right thing.”

Johnson's father maintains a residence in Greece and the Prime Minister also has Turkish roots.

“By returning the Elgin Marbles, the United States sees an opportunity for Boris Johnson to go down in history as a statesman who respected both Britain's past and projected a new confident post Brexit Britain to the world,” the letter said but there was no report whether he read it or cared.

It is thought that Parliament would have to change the law to return the Marbles to Athens as the British Museum Act of 1963 bans any property being returned, even if it was stolen from countries the UK ruled as colonies, pillaging their cultures.

A new Acropolis Museum opened in 2009 with a top floor designed to hold the marbles, a soaring glass-walled structure that has a direct view of the Parthenon from which they were ripped off.