MANY people know that the so-called "Elgin Marbles" in the British Museum are separated, by a long distance, from the Parthenon in Athens to which they belonged.

What is less well-known is that a roughly equal proportion of the sculptures of the Parthenon are still in Athens: there are the pieces which Lord Elgin decided, for various reasons, to leave behind; and there are the pieces which he simply missed because they were still buried in the ground, but which came to light later. These pieces make an interesting comparison with the sculptures in London: in some respects, they are in better shape today.

What should be done? The British Committee for the Reunification of the Parthenon Marbles, since it was set up in 1982, has argued that there is only one right answer, to bring the two halves together; the British Museum, on the other side, has sought to detach the "Elgin Marbles" from their original source and argues that they have become a self-contained, independent work of art.

This disagreement is summed up in the differing use of the word "context": for the British Museum, it means the context in which the sculptures are exhibited in Bloomsbury, alongside the sculptures of the earlier civilisations of Egypt and Mesopotamia; for their opponents (and I think for the general public) "context" means primarily the place where, and the setting in which, the sculptures were found.

This second context is a building which is still well enough preserved and restored to be an icon, not only for Athens and Greece, but for Western civilisation as a whole. Many of the sculptures in London were forcibly and destructively detached from it, so that they cannot be directly reunited with the building today.

But they can be reunited with their counterparts in Athens, in the New Acropolis Museum (due to be completed in just over a year's time) which has been built for this purpose. What arguments are deployed by the two sides in this debate? Many of the British Museum's claims are either unfounded, or have now become obsolete.

"We own the Marbles because Lord Elgin fairly bought and paid for them" - but he did not. "More people see the sculptures in London than in Athens" - no longer true. "The Greeks would not look after the sculptures properly" - this one is a case of "people living in glass houses..." What happened to the London sculptures in 1938, when they were attacked with chisels and abrasives to make them look whiter, has no counterpart with the Athens pieces, as was shown particularly in 2004 when the West Frieze of the Parthenon, which Elgin had left in place, was first exhibited (after a long process of conservation) on the Acropolis.

Nor has there been anything to compare with the catalogue of minor breakages in London, between 1960 and today, which have just come to light under the Government's Freedom of Information Act.

Finally, there is the weakest argument of all: "It would be no use returning the London pieces to Athens because nine other museums in Europe also have pieces" - yes, but Athens and London hold 98 per cent of what survives, and in any case some of the other museums have indicated that, if London made a move, they would follow suit.

On the other side, the British Committee does not chop and change its arguments - its case has always been based on the fact that the Marbles were forcibly detached from their context - but is prepared to discuss a variety of solutions, whereby the sculptures can be exhibited in the best possible way. There are legal and constitutional problems about reuniting the Marbles, but the Greek government has put forward flexible solutions to these.

The key to a solution, and the future of international museum policy generally, lies not in confrontation but in collaboration, between museums and between governments. A sign of the times is that there are now 11 other countries which have set up committees corresponding to the British one, and with the same aim. This has become an international issue, no longer a bilateral one.