Royal Academy Summer Exhibition, Royal Academy of Arts, London<br />BP Portrait Award, National Portrait Gallery, London

An exhibition designed to reflect Britain's varied artistic talents has become more confined than ever

I'd guess that the kind of work favoured by Turner Prize judges represents a tenth of Britain's artistic output, the other nine-tenths being pictures of Venice or pears on plates. It is a peculiarity of history that this vast majority has been rendered invisible by fashion, being forced to gather in hidden places, like early Christians. So the Royal Academy's Summer Exhibition does at least redress the balance of British art, bringing the output (and people) of Surrey and Hampshire to a London ruled by Sir Nicholas Serota.

Or that has been the Summer Exhibition's point until now. It is a cruelty of demographics that pears on plates etc appeal largely to the over-65s, and that the over-65s are a transient band. So the academy's recent strategy has been to mix the usual watercolours with work made – or at least chosen – by newly co-opted academicians, among them such unlikely figures as Tracey Emin RA.

Each year, the scenes of Venice grow fewer and fewer, the works of Tate Modernists ever more. In this year's summer show, the former are confined to two mean spaces – the Small Weston Room and Room X – where they hang with the mad air of Bowes-Lyon aunties in the attic. More prestigious spaces are given over to more famous artists: thus the show's first two rooms are hung with the work of the recently dead R B Kitaj, while another has been curated by Emin. The new RA apparently wanted her space to be "extreme" – ho, hum – an effect she has achieved by filling it with a hairball of pink dildos (Noble & Webster) and an automaton of a zebra shagging a woman (Matt Collishaw).

Now the question arises: what the blazes, as Tracey might say, is this all about? If the new Summer Exhibition is meant to suggest a grand continuity, a congruent Britishness, between the works in the Small Weston Room and the works in Emin's room, then it fails appallingly. What you might call Goldsmiths art and all other kinds are shown separately, for the good reason that they have nothing in common. If the summer show is meant to alert us to the fact that there is a lot of art about, then ... well, yes, and?

As in any souk, there are good things, of all stripes, dotted among the bad. Even the Small Weston Room contains a treasure, in the form of Robert Dukes's Quince. In Room IV, there's a fantastic, edible abstract, Marron Glacé, by Mali Morris. And Emin does score one point for including a large and fine Julian Schnabel in her room, a reminder that we all thought Schnabel great until Robert Hughes got his mitts on him. But you can't help feeling that the Summer Exhibition should be allowed to take a leaf out of Kitaj's book, and quietly kark it.

One of the few things in the show's favour, in fact, is that it contains almost no portraits. This is presumably because they are all down the hill at the National Portrait Gallery, vying for the annual £25,000 BP Award. I have long argued that the NPG should be shut down and its space handed over to the National Gallery. The French and Americans live without a portrait gallery: why shouldn't we? Having one only panders to the Hello! magazine cult of celebrity, and God knows that needs no encouraging.

More to the point, the whole idea of the portrait is dead in the water. As Andy Warhol noted, we live in a day that celebrates the ephemeral. Of all modes of painting, portraiture is the most outmoded, the most embarrassing. This is amply proven by the 2008 BP Portrait Award Show, whose entrants do everything but balance balls on their noses in an attempt to look modern and relevant.

The favourite trick, played by roughly half the artists, is photorealism: witness Peiyuan Jiang's portrait of what looks terrifyingly like Heather Mills McCartney. Other gimmicks are elaborate back-stories (Nina Mae Fowler's portrait of Carlos Acosta), putting subjects in odd poses (Nerys Davies's shut-eyed Mike Figgis) or filling the canvas with extraneous information (phrenology heads, salmon, Stars of David). The only work in the entire show that struck me as having anything going on below its surface was a deeply traditional, Uglow-ish portrait by one Alejandro Marco Montalvo. As for the rest: oy.

Royal Academy of Arts, London W1 (020-7300 8000) to 17 August; National Portrait Gallery, London WC2 (020-7306 0055) to 14 September