Devilish detail

After first glance at the £4.2 million revamped Camden Arts Centre, which opened last Saturday, you'd be forgiven for wondering whether its architect had bothered much with it at all. Where, you might wonder, are the tell-tale marks of genius without which no self-respecting cultural building can be complete? Where is the gravity-defying structural wonder, or the skewed thingummy, or the wonky whatnot born of the inscrutable creativity of some maestro? Where is the Bilbao effect?

It is not even satisfactorily minimalist. Minimalism, as practised by the likes of John Pawson, is about the aggressive exclusion of anything distracting, so that you are left contemplating the power of sheer emptiness. In the Camden Arts Centre stray fire-exit signs and non-matching details and old bits of decoration are tolerated. Here it just seems that there is nothing very much by way of architectural ideas. It seems modest, to use a catch-all architectural term that usually translates as "boring".

Except that its architect, Tony Fretton, is not modest. He speaks quietly, but he looks a little like a retired boxer, and has an air about him of restrained force. He starts a lot of sentences with "I", and gives the impression that he will do what he wants to do, regardless of other people's opinions. "I want to change London," he once said, "I want to make it into an exotic city."

Born in Hackney, raised in Essex and Uxbridge, and the son of an electrician, he prides himself on his directness. "I do things. That's how I am," he says, or "I do what I believe is useful and right." Or, "I'm really sick of star architecture. It stops you from doing things." At the same time, Fretton, who once wanted to be a painter, can also talk with conviction about the nuances of colour in Matisse.

Fretton is a late starter. Now pushing 60, he has been building his own projects for slightly more than a decade, having served his time in big architectural practices (and also done a stint as a performance artist). Each of his projects, however, has had an impact far beyond its scale. In London he designed the Lisson Gallery off Lisson Grove, a big, white, confident building that was a blast of fresh air in the stagnant early Nineties.

More recently, he built a substantial red-stone house in Chelsea, whose bluntness caused some perturbation in this genteel neighbourhood, but which settles remarkably well into its pretty surroundings. Last year Fretton won the competition to design the new British Embassy in Warsaw and there is a sense that his time has finally come, even if the embassy is currently being held up by security worries, in the aftermath of the Istanbul bomb.

His buildings work through the choices he makes about simple things many people would scarcely notice: a door in an unexpected proportion, a ceiling set surprisingly high, or views granted and denied by the placing of windows. In the Lisson Gallery, one of the galleries is half sunk into the ground, with a big window looking straight onto the pavement outside. This puts people inside in a strangely intimate relationship with the lower legs of passers-by. It may not sound clever, but it creates a powerfully direct relationship between the art in the gallery and the street outside.

Other architects demand that you look at their buildings. Fretton uses his buildings to make you look at the things in and around them, unobtrusively but emphatically, as a film director might cut and edit a film. These buildings can look a little awkward and ungainly, as if the smoothness and perfection that other architects aim for would get in the way.

At the Camden Arts Centre his task was to make an amiable, vaguely Tudor building, originally built in the late 19th century as a public library, into a place with 21st century standards of facilities and access for the disabled. It has been an arts centre since the 1960s, offering both memorable exhibitions and studios for drawing classes and crafts. It is placed in somewhat anonymous territory on the edge of the Finchley Road as it rushes towards the motorway, the last point of culture, as Fretton puts it, until you get to Birmingham.

The original building had a closed-up feeling, like the suburban houses around it, and a big curving staircase rising to a first floor entrance. Fretton has opened it up with a new, glassy entrance at ground level, that allows you to look right inside. Around here, where everything else is impermeable and buttoned-up, the effect is telling. It also makes the old staircase redundant and strangely romantic, like a folly in a Georgian garden