It's Time to start talking about the Elgin Marbles again. Or rather to start talking about the "Parthenon Sculptures", because the stones in the British Museum are only a part of a whole, and much of the rest is still in Athens. It is time that the sculptures in London went back to Greece.

This is an ancient argument. Ever since the British Museum acquired the marbles from Lord Elgin in 1816, there have been passionate British voices pleading that they should go back to Athens. But the argument seemed to be gradually working its way to a conclusion by early 1997.

The Greeks had met most of the traditional objections. A new modern Acropolis museum to house and protect them is being built, the British Museum would be provided with a full set of casts to replace the originals, and Britain would not be asked to pay for moving them. The museum still disagreed. But public opinion in this country seemed to be shifting decisively in favour of a return, and 109 MPs in the last Parliament - including 10 who are now ministers in Tony Blair's administration - signed an Early- Day Motion for restitution.

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Then, suddenly, the process jerked to a halt. Almost within hours of Labour's election victory, Chris Smith, the new minister of culture, told a questioner that the marbles were "an integral part" of the British Museum, and their return was not on the agenda. The Greeks were shocked; the British Committee for the Restitution of the Parthenon Marbles was appalled. And there, for the moment, things rest.

But they won't rest for long. A new edition of Christopher Hitchens's book The Elgin Marbles, revised and updated, will go on sale early in the new year. Reading its proofs - the most convincing case for return since Byron's furious protests - made me go back to the museum last week and have another look. To be honest, I have always respected the marbles but never loved them. Yes, it's a miracle that they survive at all, after 2,500 years. But the mutilation and the gaps, the handless arms and headless necks, fill me with horror. The Turks, Byzantine-Christian vandals, Lord Elgin's klutzy workmen and over two millennia of weather have all chewed and chipped and scraped away at the great friezes and the statuary of metopes and pediments until what remains feels as much an atrocity as a masterpiece. Complete, or even less damaged, those solemn processions of young men and girls, doomed oxen and raging horses would be one of the world's wonders. As it is, I get more out of the vulgar battle of the Titans on the Pergamon altar in Berlin. At least they are mostly there, and you don't have to struggle with the "how it must once have looked" enigma.

When one nation appropriates the treasures of another into its own culture, you have to ask what the new owners get out of it. It's been the custom to scold the modern Greeks for their "irrational" wish to get the sculptures back. Sir David Wilson, then director of the British Museum, declared nine years ago on television that the Greek demand was "cultural fascism ... it's nationalism, and it's cultural danger". Leaving fascism aside (not least because the Greeks have suffered a great deal more of it than the British), this implies that British possession of the Parthenon Marbles has been a matter of quiet, balanced appreciation. Not so!

The marbles were transfigured into supporters of British 19th-century imperial identity. They helped to confirm, for instance, the idea of Britain as the universal civilising force. The Victorians disliked comparisons with Imperial Rome - too much crude force and debauchery. Instead, they preferred to fancy some continuity with the world of classical Greece. They imagined this "Hellenic civilisation" as dominion founded on cultural and moral superiority rather than on crushing military strength and modern industrial technology. (That was a travesty of history; the power of Athens rested on victorious war and the export of high-quality manufactures, not on Socrates and democracy. But national and imperial myth is usually made of travesties.)

Then there was the style of the sculptures. The Victorians adored "naturalism". All other styles were seen as primitive; art had its own law of development which led upwards until it culminated in a photographic realism based on exact reproduction of the retina-image of human anatomy. After all, the art of the Empire's native subjects in benighted continents always "deformed" natural objects. The bronze-workers of Benin, the Canadian tribesmen fashioning totem poles, the Bushman cave-painters or the Maori carvers were highly skilled in their own ways but apparently unable to produce an accurate figure drawing or still life. Early archaeology showed that prehistoric peoples in Europe had been inadequate in the same way.

Plainly, Victorian Britain concluded, "stylised" art was the expression of backward, incomplete minds. Only the classical Greeks, and by imitation the Romans, had previously achieved artistic mastery - exact reproduction. So naturalism seemed to be the art of imperial destiny, prefigured on the Parthenon.

And the bodies on the Parthenon Marbles - they were pulled into the Victorian myth as well. Those bodies were young, physically perfect, mostly naked and mostly male. They suited the late-Victorian imperial cult of (male) youth and strength and decency - mens sana in corpore sano. Again, the pagan and "native" cultures of the Empire almost all allowed for customs abhorrent and indecent to Victorian Christianity, and this moral backwardness was in turn associated with their inability to achieve realism in art.

In short, the Greek wish to have the sculptures back is not nearly as weird and mystical as the British passion to keep them has been. It's a bit like attitudes to the Stone of Destiny. The Scots wanted it back, on the rational grounds that it had been pinched from them in the past. But it was the English who turned out to have charged the Stone with magical powers in the Coronation ritual, and it was the Dean of Westminster - not the Scots - who protested that it had "religious significance".

But that passion for the marbles is ebbing. I think that it's no accident that public interest in them has declined steeply since the end of Britain's colonial empire. The British self-image has changed, and the marbles are no longer required to prop it up.

"Integral" to the British Museum? As Christopher Hitchens points out, it's a striking word. If the sculptures are integral to anything, it is to the Parthenon - and literally so, for many of the reliefs were carved into the building itself rather than clapped on as decoration. This means that the marbles are not isolated "art objects" on their own, but part of something else. And that, in turn, punctures the objection that their return would set a precedent for the restitution of every "foreign" vase or statuette in the world's museums.

The British Museum has cared well for the marbles, on the whole. It has allowed the British to draw from them a special sort of national inspiration. But that particular inspiration is no longer required. The museum's moral trusteeship for the Parthenon Marbles is over, and they should now go home.

The Elgin Marbles will be published by Verso.