Duran Duran, Forum, London

An intriguing question hangs over the reformation of Duran Duran's original line-up. Why? What is motivating this unexpected reunion? Are the quintet back to milk the nostalgia market? Or are they trying to prove their musical credibility, long forgotten amid the videos and yachting disasters?

At the original quintet's first UK gig since 1984, even Duran Duran seem unsure. Their 1986 hit Notorious mutates into a cover of Sister Sledge's hen-night favourite We Are Family. And they play lots of album tracks, providing a timely, if unwitting reminder that even in the pre-Simon Cowell era, pop bands' album tracks were rarely much cop.

The audience offers the first sighting in two decades of the Duranies, once pop's most fearsome fans. Their middles may have thickened, but their enthusiasm is undimmed. They scream when the band takes the stage and don't let up until Simon Le Bon makes a little speech.

It is the little speech that no one at a reunion gig wants to hear, the one that goes: "We're going to play some new material." At most nostalgia shows, that announcement has the audience stampeding to the exits. It's testament to the Duranies' fortitude that most of them stay put.

Nevertheless, the new stuff is a slog. More surprisingly, some of the old stuff is a slog, too. Notorious and Is There Something I Should Know? prove that, despite the exotic video locations and dalliances with supermodels, Duran Duran never quite transcended their Brummie roots. Ugly, clumsy and monolithic, their attempts at funk had something of the Bullring about them.

Still, the smart pop of Girls on Film and Ordinary World sounds appropriately ageless. And it's hard not to admire the chutzpah that enables Le Bon, now 45, to sing their more recherché lyrics - the deathless "you're about as easy as a nuclear war" and the thought-provoking "don't monkey with my business" - with no hint of a raised eyebrow.

Similarly impressive is the obstinacy that makes the encore Grandmaster Flash's White Lines, a cover so ill-judged it killed their early 1990s comeback stone dead. Not for the first time tonight, you find yourself asking: why?