Two years, to paraphrase Harold Wilson, is a long time in art appreciation.

In 1990 the Tate Gallery produced a lavish catalogue to accompany the very successful rehang by the gallery's director, Nicholas Serota. In its foreword Mr Serota wrote that the display was tracing 'the inter-relationship of British and foreign art,' explaining that: 'Now, at a time when many different strands of contemporary British art are highly regarded abroad . . . it is perhaps time to break the rigid divisions between British and foreign . . .'

But this summer, the specialist art magazine Apollo carried a lengthy cri de coeur from Mr Serota, concluding that his 'vision for the Tate of the future' involved placing British art from the sixteenth century to the present at 'the centre of our activities', obliging the trustees to find 'new accommodation for a museum of modern art on an adjacent site or elsewhere in London'.

We can allow Mr Serota his change of philosophy, for our national art galleries have changed significantly in the past few years, provoking debate about much wider questions than whether there should be a building dedicated to the history of British art.

One such question is just what does the public expect from a museum of art; and, come to that, what do gallery directors expect?

'Should it,' asks Mr Serota in his Apollo article, 'be a static encyclopaedic display with major figures represented by two or three works and minor artists by one, as was the case for many years at Millbank (the Tate's home), or should we be presenting informed interpretations and readings of the collection by scholars and curators whose expertise may be expected to lead and create taste rather than to follow it?'

If the public's expectation has moved firmly towards the latter approach, then that has been largely due to Serota and his opposite number at the National Gallery, Neil MacGregor.

At the Tate, Serota has stripped the central galleries of false ceilings and screen walls. Since 1990, he has rehung the gallery's works every year, putting the spotlight on certain artists, showing them in the context of others working at the time, hanging fewer pictures, but more thoughtfully and imaginatively. He has cunningly given regular visitors the impression that every year they were entering a new art gallery.

Over in Trafalgar Square, MacGregor, too, had demolished some of the Sixties follies, the false ceilings that detracted from the National Gallery's natural grandeur. He also pursued smaller and less remarked-upon ideas. One was to mount side by side two paintings from the same period and on the same theme; the most recent example was Vermeer's The Little Street and de Hooch's The Courtyard Of A House In Delft. Casual visitors as opposed to practised art historians could make comparisons and begin to understand what distinguished great art from the pedestrian.

'Most people are intimidated from talking about art,' MacGregor told me, 'because of the vocabulary and sometimes the snobbery that surrounds it. But everyone has eyes and likes to form their own opinions from looking.'

The achievements of Serota and MacGregor were remarkable. Whereas before, the talking point about art galleries had been the exhibitions they mounted, now it was the galleries themselves.

So the question 'What does the public expect from a museum of art?' appeared to be getting the answer: 'Challenge, innovation, guidance and excitement'. But there was one other essential requirement; and after three rehangs at the Tate it began to dawn on the public and on art critics that it was not being fulfilled.

It was the expectation of seeing 'old friends', the works for which the gallery was internationally famous. For visitors from abroad this was particularly true.

This year for example, Francis Bacon, Lucian Freud and Stanley Spencer, names that visitors from abroad might journey specifically to see, are not there. The presence of one or more at the Liverpool Tate, while a welcome sign of a committed regional policy, does not make up for their absence from London.

Serota is clearly conscious of this problem, and he promises a major announcement this autumn about enlarging the gallery.

But even before he has got the space, his intentions are clear. He wants to separate the British and foreign collections. And here he could be entering troubled waters.

The Tate's role, particularly to the casual visitor, is a confusing one: the home of the history of British art, and also the main repository for international modern art. The latter role dates from the National Gallery trustees' memorably phrased decision in 1915 to move modern foreign art to the Tate to avoid 'any idea of experimentalising by rash purchase in the occasionally ill-disciplined productions of some contemporaneous continental schools whose work might exercise a disturbing and even deleterious influence upon our young painters'.

The result is that at present more rooms in the Tate's main building (leaving aside the Turner bequest in the neighbouring Clore Gallery) are given over to international modern and contemporary art than to the British collection. Robin Simon, editor of Apollo, bewails that while countless Hogarths languish in the storage racks 'a large room contains a row of advertisements for British Leyland by the German artist Hans Haacke. Why is so much space required for stuff of this kind?'

If Serota moves the international modern art to a new building and devotes the Tate as we know it to the historic British collection, he will answer criticisms of this kind. He will also, it is worth noting, be refuting the view of art history disseminated for many years by the all powerful Courtauld Institute, that British art was ever a minor school on the international scene.

But there are drawbacks to the Serota plan. Most importantly, London needs a major museum of modern art. For many it is the Tate's chief attraction. My own hunch is that a visitors' survey would find that more come to the Tate to see Andy Warhol than to see Wright of Derby. Serota must be careful to ensure that modern international art retains its high profile, if moved to a separate building, and is not downgraded.

The main building at Millbank is, argues Serota, best suited to the display of the large-framed British canvasses than to the modern works. But here he must be careful. The association, particularly in the minds of the young, is of the Tate and modern art. Banish the international modern art and who knows how much of the audience he would lose.

Second, there are those who see the separation of British art as a retrograde step. Geraldine Prince, who lectures in art history at Edinburgh University, says: 'It is almost incredible that he can consider doing it at this moment. He is making the point that British art isn't part of the European development at the time when Britain is moving closer to Europe. We should be looking at shared interests in colour and form that cross national boundaries. Yes, give British art plenty of hanging space, but integrate and show that there's a common European culture.'

Third, just how representative a history of British art would his history be? Virtually every day the information desk at the Clore Gallery is asked for the location of Turner's The 'Fighting Temeraire'. The answer is at the National Gallery.

Equally, the Victoria and Albert Museum holds some of Constable's greatest works. Just how many people go to the national museum of design, textiles and ceramics to see paintings by Constable it would be interesting to know.

So if we are to separate the British and foreign collections at the Tate then perhaps it is time for the gallery directors and, not unrealistically, the Government to sit down and rethink their respective roles and whether they are going to co-operate in presenting a proper history.

Serota's plan has other drawbacks. There is much to be said for studying British art in the context of foreign developments, pop art being a notable illustration. What does Serota intend for modern British art, of which pop is a part? Will that be in the British or the modern international collection?

These are questions for the debate that is now sure to follow. But the drawbacks do not seem insuperable, particularly if the displays encourage the visitor to make comparisons with other collections, if international modern art is given a distinguished contemporary building as its showplace, preferably on the Millbank site with which it is so closely associated, and if our leading art galleries see it as the moment to redefine their roles.

There remains something rather attractive about the idea of the British capital housing a proper history of British art; one that could enable both expert and layman to analyse afresh a part of our cultural history.

(Photograph omitted)