Who are you looking at?: It may house the world's most impressive collection of its kind, but the National Portrait Gallery is in need of a face-lift, argues Iain Gale

It's an unassuming building. A doorway on the corner of Charing Cross Road. There's no grand portico. The National Portrait Gallery is built on a human scale. And so it should be, for as the world's greatest museum devoted to portraiture, it is a showcase for humanity, exploring the ways artists have looked at that most fascinating of subjects - mankind.

Well, that's what it should be. The reality is somewhat different. As you leave your bags at the cloakroom, don't forget to pick up a free floor-plan. 'The gallery,' it advises, 'houses a collection of famous faces in British history.' If that sounds facile, avoid the temptation to throw the leaflet away. It's your only means of making sense of a gallery which, while it boasts the most impressive collection of its kind in the world, presents it in an ineffectual manner based on an obsolete, conceited premiss.

The floor-plan suggests that you begin on Level 5. The lift opens on a long gallery of notable Elizabethans, well labelled with information on the sitters. That there is little about the artists comes as no surprise. This is, after all, the age of the 'unknown'. Portraits are displayed above glass cases of prints, and the whole resembles a country house rather than an urban gallery. The illusion ends abruptly in Room 2 ('The Early Stuarts'), whose obtrusive lighting and exposed Victorian girders re-state the museum environment, encouraging a swift move to the English Civil War room, which, despite some fine paintings, is also cold and institutional. But here a deeper malaise becomes evident. The hang is chronological and the labels are concerned not with art but with history. Uniquely for an art gallery, the subjects' names appear at the top, in capitals, with those of the artists placed beneath, in upper and lower case.

The 'Restoration' room pictures, hung en masse, invite less attention than the portrait of Queen Anne that beckons from an end gallery, even though suffused in a ghastly yellow glow. The presence here of Kneller's virtuoso allegory of the Duke of Marlborough is uplifting, but this too suffers from lack of interpretation. Next door, though, the artist's portraits of the Kit Kat Club members are hung sympathetically, in their own panelled corridor.

Yet disappointment waits just around the corner. There is appallingly little here of the 18th-century highpoint of British portraiture. Granted we have Reynolds' portraits of Banks and Sterne, but mere likenesses of the famous tell the visitor little of this vital moment in the development of portraiture. There is scant evidence of the informal conversation piece and none whatever of the seminal theorising of Richardson or Reynolds. Surely Reynolds and Gainsborough each deserve a room of their own? And what of Hogarth? Clearly this is not a gallery for informality, or images of the 'lower orders'.

Instead, we have the 'beautiful and elegant' Regency Room (which is neither, on account of a garish green carpet that dazzles the eye), and, adjoining it, the prosaic divisions of the 'Struggle for America' and 'Britain becomes a World Power'. Herein lies the gallery's raison d'etre. At the entrance you might have noticed a gold-lettered inscription: 'There cannot be a greater incentive to mental exertion, to noble actions, to good conduct on the part of the living than for them to see before them the features of those who have done things which are worthy of admiration, and whose example we are more induced to imitate when they are brought before us in the visible and tangible shape of portraits.' Lord Palmerston's Westminster speech on the gallery's opening in 1856 owed much to an idea of teaching greatness by example, derived from Petrarch, Castiglione and Sir Francis Bacon. It is this that makes the idea of a national portrait gallery uniquely British. It is, in effect, one of the last relics of Victorian jingoism.

Further evidence is a lift ride away, deep in the gallery's Victorian heart, among cheerless, stereotypical portraits of Empire- builders and scientists. The history lesson leads on to the canopied splendour of Edward VII, who stares uneasily at portraits by Augustus John and the Camden Town Group, absurdly hung opposite Sargent with no explanation of the dichotomy which characterised the art of the era.

With the landing devoted to portraits of our present Royal family, the historical framework begins to lose coherence. Close by, in the early 20th-century galleries we meet Churchill, caught smoking by Sickert, and above him George V lighting up, in an image popularised as a postcard. But nowhere is an attempt made to explain how two such icons differ in intention or meaning. The First World war is summed up by a marble figure of T E Lawrence, recumbent at the foot of Sargent's huge group portrait of incompetent generals. Here, the war of the common man still belongs to the statesmen of Guthrie's massive portrait, hung on an ugly screen that confronts, illogically, a portrait of Monty in 1944. These galleries are a mess. Unless you know what you're looking for, there's not much incentive to continue into the dead-end of 'The Establishment, Science and Theatre 1914-1945'.

Below, on Level 1, lie the much lauded new galleries, opened last year. They're a pretty Post-Modern essay in blue marble and white paint, but no better planned than upstairs. The walls are overcrowded and the Victorian categories persist in a corridor of 'Politics, the Performing Arts and Sport from 1945' and rooms for 'Science, Technology and Business' and 'Late 20th-century Arts'. The only change is that history appears to end in 1945. Why, after 'Britain Becomes a World Power', we wonder, is there no 'Britain's Empire Disintegrates'? And here is the Queen again, this time in a Warhol multiple. No prizes, though, for why she's not upstairs with the other Royals.

And that's it. The visitor leaves with many unanswered questions. Not least: 'Why paint a portrait?' What rankles most, though, is the lack of attention paid to the artist. Wilde wrote: 'Every portrait . . . is a portrait of the artist not the sitter.' This truth is borne out by comparing Annigoni's Queen to that of Warhol or considering portraits by Hodgkin or Bacon, neither of whom, incredibly, are represented here. While individual artists are explained in temporary exhibitions, these seem antithetical to the permanent display. The gallery has just released record- breaking attendance figures. Publicity has made the new look a success. People want to come - but how many to increase their 'good conduct'? Today's viewer seeks an understanding of the subject; that requires an understanding of the artist.

It's time for a rethink. A gallery of the 'Great British' is superfluous. This child's history lesson should be a sideline; the gallery's true purpose is an explanation of portraiture, the most English of art forms. We should be proud of the NPG for the art it contains rather than as a hubristic reflection of past glories. Blake asked, 'Of what consequence is it to the arts what a portrait painter does?' and portraitists have long suffered from the stigma. In its present state, the NPG does nothing to relieve that status. It is merely a wasteful, maddening anachronism.

(Photograph omitted)