After 21 years and shows that have stretched from Wagner's Ring Cycle ("four magnificent operas in 1 hour 15 minutes") to The Messiah (first produced in 1983 and revived last year at the Bush), the National Theatre of Brent have finally arrived at the National Theatre of Great Britain. Desmond Olivier Dingle - who founded the company, runs it from his home "in bustling Dollis Hill", and has co-written and co-starred in every one of their two-man epics - is a glorious composite of overreaching ambition and overstated pomposity. Meanwhile, unpaid sidekick Raymond Box is the picture of eager incompetence.

In the company's final part of a sex trilogy begun in 1984 with The Complete Guide to Sex and continued with The Mysteries of Sex in 1997, they now offer The Wonder of Sex in their most complex staging yet. A futuristic, state-of-the-art set by Francis O'Connor comprises all-white surfaces and gleaming television screens, onto which are also trucked many and various set pieces, from Freud's psychiatrist's couch to a rustic cottage for an enactment of a scene from Lady Chatterley's Lover. In the process, they have commanded the full technical resources of the National Theatre.

Their own theatrical resources, however, are as keenly threadbare as usual. For those already familiar with their work, none of this will come as a surprise. In fact, regular visitors - and I count myself a fan - may find that some of the routines are becoming a little over-familiar. There's the inevitable loss of Raymond's wig, the invariable walking out of one or the other from the show, and a protracted audience participation scene that on this occasion involves an enactment of the Russian Revolution.

If, however, you are lucky enough to be new to their work, this will all be relished. In fact, the joy of seeing the NT Brent elevated to this large stage after being more accustomed to finding them in places like the Bush and Tricycle, is to see how the comedy plays just as adeptly in a bigger space. Patrick Barlow and John Ramm, the two brilliant comedian actors who inhabit Dingle and Box respectively, are in total command of the Littlewoods stage (as Dingle insists on calling the Lyttelton), if not the effects that, as always, spiral out of control.

At nearly two and a half hours, however, you also can't help feeling that they've possibly over-extended themselves a little. But that's to be churlish, since the whole point of the NTOB is that that is precisely what they do.

For my part, I was left wondering: What next? Is it now time for The Reduced Shakespeare Company to take the place of the RSC?

- Mark Shenton