Within: New Photographic Portraits, Bloomberg Space, London

Ranks of portriats of uniformed band members show that clothes don't always make the man

I forgot to count how many members of the Black Skull Corps of Fife and Drum Roderick Buchanan has photographed for his new work of that name, but let's hazard a guess and say lots – 30, maybe?

The Corps is a Glasgow marching band: its website comes up marked "Restricted", with a box announcing its attachment to "the Loyalist / Unionist community of the United Kingdom". Buchanan has shot each member of the band in the same face-on pose, printed the results in identical 80x62.5cm prints and framed these in unvarying white wood frames. Wearing the same frogged uniform and expression, the portraits march at uniform height and interval along two walls of the Bloomberg Space, part of a show called Within.

On inspection, there are differences between the various band members – one is wall-eyed, one looks like Arthur Mullard, another like Marc Quinn before he lost weight; three, clustered together, are children – but their insistent same-ness means you pretty much overlook these. It is as if a school photo has been broken down into parts; you half expect one of the men, Andy MacAdam maybe, to appear twice, having snuck around the back while the pictures were being taken. About a third of the way along is a white barge-board painted with the words "Scottish by birth, British by the grace of God", and the subjects' names appear in identical sans serif letters beneath their respective pictures.

And what is all this about? It is a given of post-Renaissance art that portraits should reveal their subjects' inner lives, externalities spelling out internalities. This belief makes modern assumptions about individualism, the primacy of the one over the many. But what happens when the subject of a portrait has chosen to cash in his individuality in favour of collective bargaining? Beyond this question lie bigger ones: as social but selfish animals, are we not all members of the Black Skull Corps of Fife and Drum, or some variant of it? To be genuinely revealing, shouldn't portraiture record sameness as much as difference?

In bringing together a number of artists whose preoccupations revolve, to a greater or lesser extent, around issues of this kind, Within hints at something afoot in the zeitgeist – a tendency of people to cluster in groups when times are hard, perhaps. That might be worrying (remember Germany circa 1933?), except that four photographers do not a historical tendency make, especially when one of them – Sarah Jones – doesn't really seem to fit in with the other three. Quite why Jones's fashion-grunge shots have been included in this show, I cannot say. They seem to me empty, and not in a good way – the exact opposite of Buchanan's, which are brilliantly vacant.

As to the other two artists in the show, their work puts you in mind of Freud's words in Civilization and its Discontents – a study of the paradox of selfish humans forced to live in selfless societies: "One is inclined to say that the intention that man should be happy is not included in the plan of Creation."

Muzi Quawson's The Hissing of the Summer Lawns is a slide-show, projected on a wall, of an average-to-redneck family in Georgia going about its daily business – the mother shopping at a mall, the father and a friend doing something to a flat-bed truck; the daughter eating a hamburger, the son, overweight, sitting around and talking on his mobile phone.

I suppose this could loosely be described as group portraiture, although we have no way of knowing whether the players in Quawson's non-drama are actually related to each other, or even whether the whole thing has been staged. What's interesting isn't her projection but our own – the way we set up social structures and interrelations to make sense of what we're seeing, re-inventing life according to our experience of it. The Hissing of the Summer Lawns is Big Brother for artfolk, the image not so much of a family as of the audience that looks at it.

As to the wonderfully-named Poppy de Villeneuve, her black-and-white prints of nameless people put up against a wall call to mind Susan Sontag's observation that the word "shoot" is applied both to cameras and guns. The camera may never lie, but that is not the same thing as saying that it always tells the truth. What de Villeneuve's tells us – what this show as a whole has to say – is that there is no truth to be told; that portraiture is an impossibility, as is the state of man.

Bloomberg Space, London EC2 (020-7330 7959) to 7 Feb