It is the custom now for institutions concerned with the visual arts or responsible for comment on them to avoid old-fashioned honest criticism by critics who have some intellectual standing in the field.

Order of merit: Diarmuid Kelley’s I went to a marvellous party — so much deeper than its frivolous title — offers hope for portraiture

Instead, they enlist the subjective judgments — often uninformed opinion — of politicians, comedians and notorious talking heads, none of whom knows anything of painters, sculptors or the practical business of exhibiting their work, and whose prattle is irrelevant and misleading. From writers they commission minor works of literature inspired by works of art — a phenomenon known as ekphrasis to the ancient Greeks — but while this may have contributed to the recovery of the essay from a near-death experience, it has done little to help us understand the works of art that were the essays’ kindling.

For years the National Portrait Gallery has invited scribblers to contribute their thoughts to the opening pages of the catalogue of its annual Portrait Award. For 2010, its guest is Rose Tremain, distinguished novelist, who teases us with the thought that the portrait of which she writes may not be real but just another of her mind’s “provocative inventions” — though I must argue that it is not provocative, but was provoked.

For once I am grateful to the essayist, for she illustrates a point with the reproduction of a photograph of Alan Bennett — not a painted portrait, but a photograph adopting a now common apparatus of contemporary portraiture. Its resemblance to painted portraits is startling in its modern mannerisms: Bennett is dropped to the lower half of the composition, a head, hand and shoulders set against a mantelpiece so much cluttered with sentimental memorabilia that his full-frontal mask is almost just another object.

Friendly face: David Eichenberg’s portrait of a friend, photographic even to the unfocused blur won the third prize this year

Does this clutter reveal secrets? Are the photographs and postcards the subtexts of a less public life unknown to those who know him only as the serene, wry, shrewd performing commentator with a polished northern drawl? I ask because the winner of the third prize this year, David Eichenberg, in adopting (far less specifically) this very formula, claims that in its detail his portrait is to be read exactly as we are meant to read Holbein’s portrait of The Ambassadors in the National Gallery, a telling inventory of intellectual interests and possessions.

Eichenberg might just as well have submitted the photograph on which his portrait is based, for the labour of copying it in paint with brush is wasted when they are so much the same; so too might the winner of the second prize, Michael Gaskell, and the twenty or so others who have, as painters, contributed nothing to their feeble photographs and perhaps even adulterated what minute quality they had. Professional photographers make a better job, not only of composition, lighting, angle, focus and all other technical aspects of their work, but a better job of the character and insight that should be the prime purpose of these happy-snapping portrait painters.

That the Portrait Award is no longer what it was when it began under what became the tainted sponsorship of John Player — a perhaps now forgotten manufacturer of cigarettes — has been evident for some years. We have only to look, not just at the prize winners in those early days, but at the general body of exhibited portraits, to see how far the Award has fallen in quality, invention, surprise and the comforting reassurance that initially grew from it that portraiture was not yet dead. There is no such reassurance in the exhibition now. If this year’s selection — of 58 from 2,177 entries, the largest ever — is in truth the best the judges could find, then the worst must have been beyond words contemptible.

The director of the NPG has it, however, that the exhibition is “a glorious celebration of contemporary painted portraiture”. Tony Hayward, the chief executive of BP, the even more tainted sponsor whose name has been attached to the award for 20 years or so, and whose purposes are to exploit it in their advertising campaigns and harvest free column inches of lamentable comment in all our daily papers, tells us that “as always, the quality of entries is outstanding” and the exhibition itself is “testament to the great talent that the Award uncovers”. BP’s Director of Arts and Culture, Des Violaris, proclaims that “the invention and quality of this year’s entries have yet again surprised and delighted us”.

Such mendacious conceit does the Award no good. Anyone with half an eye can see that it has run into the sand — indeed I said so when I was a judge five years ago, suggesting that only if the Award were rejigged and the judging sharpened could it reasonably continue. I argued then and argue still that the crass amateur must be discouraged, for I am convinced that the exhibition of so much dross must deter many serious painters who do not want their work shown cheek-by-jowl with rubbish. I argued that the age limit of 40 should be abandoned — and this was done. Now, however, I think I was in error, for the first prize — £25,000 — has this year been awarded to Daphne Todd, a past president of the Royal Society of Portrait Painters who, at 63, can hardly be short of esteem and the commissions for which one so eminent can charge that sort of fee.

The worst thing that could possibly happen to the Portrait Award is that it should become indistinguishable from the annual show of that Royal Society. I was also inclined to support the suggestion that the Award should be open to painters living, working and born abroad, but the foreign entries this year are deeply discouraging and serve only to give BP another statistic in the sense that portraits were submitted from 69 countries — to which the response must be, so what?

I long supposed that strictly irrelevant factors weighed heavily on the judges, and as a judge I found this to be so. BP’s representative, Des Violaris, thought too much in terms of portraits that might make good advertisements and, pursuing the political correctitudes, demanded that there must be painters and subjects other than white Anglo-Saxons; and the NPG’s director begged us to let Miss Violaris have her way, arguing that as the sponsor supplies the cash, the sponsor must be allowed the whip hand. The director himself seemed less interested in quality than in what might look impressive on the walls, not caring that the inclusion of one big bad picture might mean the exclusion of four smaller and better paintings.

And who were the judges this year? Sandy Nairne, director of the NPG, a sometime Arts Council and Tate Modern man whose eye for painting seems to have died in his progress through these deadly institutions, Sarah Howgate, a sidekick at the NPG, and Sir David Scholey, former chairman of the NPG’s trustees and a lifelong banker; the outsiders were Ishbel Myerscough, who won the Award 15 years ago with a ghastly pseudo-Indian caricature of a Venus by Titian, Christine Rew, a museums manager from Aberdeen, and the inevitable Miss Violaris, devoted lackey of BP — a team calculated to recognise which side the bread is buttered. Did they choose anything of any merit? Diarmuid Kelley’s exhausted cavalry officer (so much deeper than its frivolous title — I went to a marvellous party) and Paul Benney’s Paul Getty III are things of ambition and scale enough to offer hope for portraiture, and among the smaller things Robin Bagnall’s disagreeable Self Portrait, though lost in a poor hang, has promise. The rest are laboured nothings.

What is to be done? I am inclined to argue that the Award now has the opportunity to escape from the dead patronage of BP. Apart from all other matters in the Gulf of Mexico, the ghastly deaths of pelicans, turtles and other marine creatures, there are enough to convince me that BP is in such deep disgrace that its very initials sully everything associated with the firm. It would be wise to withdraw from its sponsorship of the arts. Some may take the Jesuitical view that the ends justify the means, but mine is that this calamity is too grave a self-inflicted wound and that years will pass before BP’s executives can expect to be air-kissed back into the marble halls of the NPG and Tate Britain, where their long sponsorship of annual change has been nothing but damaging and disruptive.

The Portrait Award is a comparatively inexpensive example of sponsorship, well worth the adoption of a sponsor more interested in art than in any exploitation to be made of it, but any new sponsor must revise the weary formula, must insist on judges who are not lackeys of either the institution or the sponsor and whose opinions artists and the public respect. The purpose of the Award should not be as a propaganda vehicle bought for cash — as it has been for BP. It was initially established to break convention’s deadly hold on portraiture and to offer patrons alternatives to the dread grandees of a dying trade; it was to encourage the gifted young not to ignore what had become a weed-clogged backwater of painting, and to give them the opportunity to find new formulae and tweak the old.

Now all these years later the only alternatives it offers are those of the crass amateur photographer so that these too have become dread familiars, and it gives first prize to so established a figure as a past panjandrum of the Royal Society of Portrait Painters. Full circle? Weary round? If it cannot be shaken by the scruff, then the only alternative is to recognise that the Award has failed its early promise and seize the opportunity offered by BP’s disgrace to put an end to it.

The BP Portrait Award is at the National Portrait Gallery (020 7306 0055, npg.org.uk) until September 19. Daily (Thu and Fri until 9pm). Admission free.