The Acropolis Museum in Athens is an architectural marvel that has rightly won awards. The way the remaining Parthenon marbles are bathed in sunlight and overlooked by the temple that was their original site is profoundly beautiful. But what I found most affecting when I visited last week was the deliberate absences in the exhibits – spaces pointedly left blank for the day when, Greeks hope, the rest of the sculptures that were carved by Phidias and his assistants circa 447–438BC will be returned.

Many readers will no doubt be aware that many of these priceless sculptures, once better known as the Elgin marbles, reside in a gloomy room in the British Museum, having been torn from the Parthenon in the early 1800s by Lord Elgin. It is a subject of great controversy, but one that most Britons, especially those who are young and not of an imperialistic bent, struggle to care about. When polled in 2014 by YouGov, only 23% of British people wanted to keep them.

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In contrast, Greeks continue to care deeply, and Brexit has provided an opportunity for their government to exercise some pressure. After all, the UK government will need approval from all EU member states if a Brexit deal is reached. Rather cannily, last month Greece’s then culture minister, Lydia Koniordou, sent a letter to Jeremy Wright, our culture secretary, requesting the opening of negotiations regarding the marbles. It’s ironic that, at a time when Brexit has revived the sort of jingoistic imperialism that turns many a remainer’s stomach, such symbols of British cultural chauvinism should be questioned.

There are many powerful arguments for returning the marbles. I would advise anyone interested to listen to a podcast of a debate earlier this year, in which Andrew George, chair of Marbles Reunite and a Liberal Democrat MP, and the actor Stephen Fry called for the marbles to be returned to Athens. They appealed to a British sense of fair play, pointing out that it would be less a humiliating climbdown, more a gesture of friendship to Greece and its people.

But the most persuasive argument came from a member of the audience, who pointed out that the Parthenon marbles were a single work of art that should not be divided. Wouldn’t it be bizarre, he argued, if the head of Michelangelo’s David was in the British Museum and the body in the Uffizi Gallery? As Greeks have been saying for years, at the moment the Parthenon marbles are like a family portrait in which loved ones are missing.

One of the arguments most frequently made against returning the marbles is that the British Museum is a museum for the world hosting global treasure. By comparison, the one in Athens is insultingly portrayed as simply a national museum – despite the millions of tourists who visit the cradle of western civilisation every year. But to my mind Brexit makes such an argument totally redundant.

Can the British Museum really lay claim to being a museum for the world when the British government has jettisoned freedom of movement in its Brexit negotiations? I think not. Send the Parthenon marbles back to Athens, and they are free to be viewed by any of the citizens of the European Union who should choose to travel there, free from restrictions. Furthermore, Greece would be happy to lend the marbles globally. Meanwhile, Britain can surely make do with plaster casts of the sculptures. The majority of visitors probably wouldn’t even notice, or care.

There are many people who regard my generation as snowflakes for wanting to decolonise education curriculums or objecting to certain statues on university campuses. But we are also a generation of remainers firmly internationalist in outlook. For us, one of the greatest moral statements our government could make to express regret for past colonialist behaviour would be to return the Parthenon marbles to their rightful owners. They won’t, of course. Conservatism is after all a commitment to old-fashioned, traditional values. In contrast, Jeremy Corbyn says that any Labour government led by him would return the marbles. He gets it.

The “slippery slope” reasoning that returning the marbles would prompt every country to ask for everything back is irrelevant – would you accept a thief hoarding stolen goods on such a basis? This is a question of doing what is right. Brexit Britain doesn’t much care about gestures of international friendship. But perhaps its hand will be forced. Whatever happens, the long-outdated case for hoarding the marbles will continue to crumble, just like plaster.

• Rhiannon Lucy Cosslett is a Guardian columnist

• This article was amended on 26 September 2018. The article originally said: “Greece’s culture minister, Lydia Koniordou, this month sent a letter to Jeremy Wright”. The letter was sent in August, not September. Koniordou was culture minister when she sent the letter, but no longer held that position when this article was published.