Leon Kossoff: Tate Gallery.

The vision of London and Londoners in Leon Kossoff's paintings stems from no identifiable reality. That this vision has, nonetheless, a certain credibility says much for Kossoff's imaginative transformation of his chosen material. Every recorder of London since William Hogarth has transmitted depictions of the city over his own particular wavelength. Hogarth trained his eye on the urban corruption of innocence, on social arrivisme and the congress of the streets; Gustave Dore showed us Victorian poverty dwelling "in rags and tears"; and Walter Sickert made the darkness of London gleam with the race for survival embodied in tawdry Camden Town vaudeville.

When Kossoff began painting the city of London in the '50s it was a postwar landscape of ration-book pallor and cavernous bomb sites, a city of excavation and reconstruction. For Kossoff, it has remained that dreary, down-at-heel, wind tossed place, its people existing on the pavement's edge, herded into the Underground, wetting their white skins in the chlorinated waters of a public pool, sitting bereft on a park bench, mortgage refused, their pet dog dead. Occasionally Kossoff has tried to lighten the mood, but Family Party, 1983, for example, turns out to be a wake for what appears to be an Egyptian child-mummy laid across adult knees. It is a lowering vision. When encountered in those isolated works where Kossoff's childhood memories inform his tottering accumulations of paint, it is not unconvincing, but when it fills eight galleries, as it did at Kossoff's recent Tare retrospective, it is dispiriting in the extreme.

It was bad luck for Kossoff that his exhibition adjoined a display of the Bruce Nauman works in the Froehlich Collection. No sign there of tame discomfort and fleeting angst. Where Kossoff longs to be thought "serious," Nauman's seriousness comes from a sharp and brilliant apprehension of life's confrontations. Where Kossoff can prove seductive, Nauman is brutally compelling; and where Kossoff provides confirmation, Nauman puts us on a tightrope, with nothing to catch us if we fall. The comparison is necessarily strained, the product of accident, but it does point up some of Kossoff's shortcomings, not least the comfortable assumptions that lie behind his sometimes arresting work.

It begins well. Great sighs of thick paint, dour and dignified, tie earth and image together; disconsolate figures in rooms are as good as Soutine's hanging carcasses. In these early works, there is a merciful absence of the skeins and flicks of light paint that, from circa 1970 onwards, cross his built-up surfaces. Until then, Kossoff is to be reckoned with, capable of taking his place in any account of postwar European art, an account that includes Jean Fautrier, Wols, and Jean Dubuffet. His individual rhythm is heard clearly above the cacophony of his influences. Regrettably, he seems to have thrown away his aces for a more narrative and conservative style, limiting tonal contrasts and imposing, especially on his figures, a wistful sentimentality. In the urban views of the '70s, the horizon line, a shard of sky at the top, becomes an indispensable mannerism. Passersby become toy-town inhabitants, fattened-up versions of the figures found in L. S. Lowry's faux-naif, Northern townscapes. Caricature devoid of humor blights many a portrait.

With changes of accent and facture and a chalky lightening of color, Kossoff's work has remained much the same - full of integrity, resolutely serious, offering neither celebration nor redemption. In the rooms devoted to the later works, two series stand out: one presents views of Hawksmoor's Christ Church, Spiralfields; the other, depicts trains on inner-suburban lines, seen from above. The former, weaving childhood memory with vertiginous spatial effects, have a particularity that is lost or obscured elsewhere; the train paintings, with their warmer color and sense of surprise, add a distinctive note to a theme treated before World War I by the Camden Town painter Spencer Gore.

There is no mention of Gore or his colleague Sickert in the long catalogue essay by Tate curator Paul Moorhouse. Kossoff's lineage goes virtually untreated save for the influence of David Bomberg, guru to a whole group of postwar British painters; and though there is an inevitable nod to his slightly younger contemporary Frank Auerbach, it is a nod of friendly intimacy rather than influence. There is no discussion of Van Gogh, Soutine, or de Kooning, of the CoBrA artists or the neo-Romantic hangover from the 1940s. You might think Kossoff had sprung fully formed from London's East End. No case is made for the recent internationalization of his reputation, which culminated in his exhibition at the Venice Biennale last year. The timing of the Tate show seems to have misfired - the gallery was virtually empty on my last visit - leaving Kossoff dangling between an honorable, circumscribed past and an uncertain future.

Richard Shone is an associate editor of The Burlington Magazine.