Titian is universally acknowledged as one of the greatest painters of the Italian Renaissance, a Venetian who in his long life not only brought renown to his native city but painted for Philip II of Spain, his powerful patron, masterpieces that for centuries have inspired and entranced generations of artists and art-lovers.

Some of the most celebrated now hang in galleries in Britain, including four that are part of the mighty Bridgewater collection, on loan to the National Gallery of Scotland. But although they have been on public display almost continually since 1806, when the 1st Duke of Sutherland opened up his townhouse on certain days, Britons may not have a chance to see Diana & Actaeon, one of Titian's greatest paintings, for much longer. Unless £50 million can be raised by New Year's Eve, the painting risks being auctioned. Could any British institution outbid an American gallery, a Russian oligarch or an acquisitive sheikh from the Gulf?

The decision to sell the painting has been taken by its owner, the 7th Duke of Sutherland. He is also to sell a second Titian, Diana & Callisto, in four years. But he has offered them first to the National Galleries of Scotland, and if this institution can meet his price, he has promised to leave the other 25 masterpieces - Poussins, Raphaels, a Rembrandt and two other Titians - in Edinburgh for 21 years.

His decision will dismay art lovers. Raising £50 million in four months would be a Herculean task at the best of times. As recession looms, companies cut their charitable donations and the Government is pressed to pay for wars in Iraq and Afghanistan, let alone rising health, fuel and social security bills, it looks all but impossible.

Disappointment with the Duke's ultimatum, must, however, be matched by understanding for his dilemma. His family have been exceptionally generous in offering the Bridgewater collection, one of the world's largest private holdings of Old Masters, on loan to Scotland since 1945, forming the core of the National Gallery's rich European holdings. But art has risen astronomically in value. The collection is now worth around £1 billion - excluding the Titians. It is hardly wise for any family to keep so much of their wealth inaccessible and unrealisable, serving only to impose vast death duties on successive generations. The £100 million offer to the National Galleries of Scotland, which are, uniquely, to join forces with the National Gallery in London to keep both Titians in Britain, is far below their market value. Dubai might start the bidding at four times the price.

The two Titians are included on a list submitted to the Prime Minister in 1973 of works of such paramount importance that they should never be allowed to leave the country. An absolute ban, however, would be wrong: it would contravene the principle of a free market (even though countries such as Italy are far harsher in stopping the export of cultural patrimony). It would raise awkward questions about how most of Britain's great holdings first came to this country. And it would probably need a special law.

Instead, the public must rise to the challenge. If people really care about masterpieces, let them sponsor, raffle, cajole, campaign and beg for the sum needed. Edinburgh, spectacularly, saved The Three Graces this way. The Titians are an infi- nitely greater treasure. Pass the hat.