To keep sweet the politicians who determine the annual grants and subsidies on which it depends, the National Gallery has over the past few years sent six travelling exhibitions to Bristol and Newcastle, drawn largely from its own collections but supplemented with pictures from the two host cities, and a handful from other sources.

This year, the seventh - and, hopefully, the last - is titled Love. Such travelling shows must have a title, no matter how specious, for no better reason than the PR departments of the galleries involved must have a tool with which to attract punters. Love will no doubt sow hopes of nudes and copulation and excite anticipation in the visitors. The title also enables the curators to wrestle every picture into the overall theme, even if it is essentially a landscape or interior, a Christian saint, an eastern goddess or a bunch of flowers.

In such a case as this, readers of the exhibition catalogue must remember that the curatorial business is carried out by officials at the bottom of the heap, the gallery's deputy assistant sidekicks cutting their teeth on casuistry. The catalogue of Love was written, a man of 70 might suppose, by two small girls of seven. Love "is at once simple and complex", they begin. "It is instinctive but inexplicable," they continue, "it brings both sadness and joy."

The sane reader suspects that the girls have cribbed this from a manual on sex published in 1935 but it is just the poor things struggling to identify a common reason for exhibiting Vermeer's Young Woman at the Virginals with David Hockney's We Two Boys Together Clinging, and Grayson Perry's ceramic rabbit (surely a hare?) with Murillo's Infant Baptist embracing the lamb.

These exhibits raise another political point in that Labour ministers of culture share the conviction that, if the young are to be drawn into an interest in old art, it must be mixed with new. Sweetened with some trash by Tracey Emin, the ancient medicines of Raphael and Rossetti will more easily go down. Again, it is not so: they do not mix, and it is the contemporary artist who suffers in the inevitable comparison when the curators claim unbroken continuity between, for example, the dramatic competence of Joseph Wright's newly-weds, the Coltman couple, and the deliberate incompetence of Hockney's clinging boys, an angry and ugly protest piece that had, briefly, some value as propaganda but no merit as art.

As for the inclusion of pictures by the twin sisters Singh, Amrit and Rabindra, these hideous reworkings, in gouache and gold dust, of the formulae of the traditional Indian miniature, are meretricious to a repellent degree; they are exhibited by the National Gallery in compliance with the dictates of political correctitude, for no mixed-bag exhibition can be presented without a patronising nod to at least one ethnic minority, no matter how feeble the offering.

This exhibition should never have been mounted. The underlying-idea is feeble, the contents forced to fit, and the choice is too diffuse to inform at sight, thus compelling reference to the arguments put forward in the catalogue, only to find that these are naïve and flatulent. With only one nude, Cranach's scrawny Venus in a fancy hat, and not a hint of copulation, I doubt if the sophisticated citizens of London will be flocking to the door.

Open tonight until 9pm. Exhibition continues until 5 October (020 7747 2885, www. nationalgallery. org.uk). Admission free.