The Government’s proposal for a new law to prevent seizure by aggrieved creditors of works of art lent from abroad for exhibition in British museums and galleries comes just in time. Unlike others in the European Union, Britain grants no specific immunity to artefacts lent by foreign museums. Last year an attempt by a Swiss trading company, which was owed some $60 million by Russia, to get its money by impounding 54 French masterpieces on their way home to the Pushkin museum threatened to halt all loans of artworks to countries without specific protection against cultural kidnapping. Unless Britain acts quickly, galleries may soon find that no one will risk sending national treasures to these shores for fear that they will become hostage in a financial or cultural dispute.

Under international law, national cultural assets are protected against confiscation. But that immunity is wearing thin. Art is now so valuable that it is an ever more tempting target for those wanting to recoup bad debts. Following the example of slapping a lien on ships sailing into harbours where creditors are waiting, lawyers see paintings as a tempting target.

The trend began in the US, where families of those whose assets were seized by the Nazis have gone to court to reclaim works they claim are rightfully theirs. The precedent encouraged others. Third World countries are trying to repatriate cultural property to improve their tourism industry. Minorities are seeking redress for imagined cultural oppression. Last year Australian Aboriginal groups obtained an injunction — later overturned — preventing the return of ceremonial artefacts to the British Museum and Kew Gardens. Some families are simply trying to make money: a lawsuit against the Los Angeles County Museum of Art in 2003 concerning 76 paintings on loan from Russia — already granted immunity before arriving in the US — demanded greater “recognition” for the descendants, by which they meant a substantial lump sum and a share in the museum’s profits.

Little wonder, therefore, that Russia has threatened to halt loans altogether. Or that museums which rely on blockbuster shows for their profits are fearful that many of the best works may now be inaccessible. Already the Tate gallery has had to cancel the planned exhibition of Constantin Brancusi’s The Kiss because it could not give Romania a guarantee against seizure by a potential claimant.

Immunity does not halt disputes over repatriation. Greece has not dropped its demand for the return of the Elgin Marbles. But if claimants resort to hijacking any artefact that arrives on their territory, or if bankruptcy courts can be persuaded to halt a convoy of lorries and seize the most valuable works, justice is short-circuited and art becomes prey to official banditry.

The lack of an immunity law in Britain points more to official sloth than principled objection. But without appropriate protection, this country will become less of a canvas for the world’s greatest artists.