Dir: Mark Mylod. UK. 2002. 88 mins.

A send-up of white kids trying to act black, Sacha Baron Cohen's alter ego Ali G has cut quite a figure on UK TV, making a fool of celebrities like David Beckham. He has shot a video with Madonna (Music). Now he has his very own film. It will be massive in his home turf of Staines and across the UK, thanks to the ubiquitous cult of Ali and a huge publicity spend. But even here, the film isn't clever enough to make much impact outside its under-25 target demographic. It should open spectacularly on a smash-and-grab basis before word gets out and will prosper on video. The story takes Ali to America, with a silly fantasy prologue in which he confronts real gangstas in an LA hood. But, so local are its comic references and so dependent on the character's established persona, that it's hard to imagine Ali commanding much respect outside his home turf.

Ali G is a lower-middle-class youth living in Staines, an ultra-dull small town West of London. Ali likes to imagine he's a cool homeboy and has an arsenal of pseudo street-talk, his own gang, the West Staines Massive, and a wardrobe of garish track suits and oversized gold jewellery to prove it.

The film begins with Ali's four-strong posse locked in a war with arch-rivals East Staines Massive for control of a playground climbing frame. Suddenly he's plucked from obscurity by the unscrupulous Deputy Prime Minister (Charles Dance) who, scheming to bring down the PM (Michael Gambon), persuades Ali to stand for parliament. The plan backfires after he somehow wins the seat and the public imagination is captured by his slogan - "keep it real" - and policies such as a 25% tax on women's underpants (excluding thongs).

The film misses a trick or two here. It could have broadened its appeal to that older audience who enjoy Ali as a social satirist by poking fun at a trend-conscious Blairite government, desperate to restore its fast-fading lustre by chasing the youth vote. Ali G IndaHouse doesn't go there. It's careful not to pin down the politics of its ruling party - if anything they're Tories (there are Conservative minister lookalikes in the Cabinet and compromising photos of Thatcher and Major in the safe at Chequers, the prime minister's official country residence). It also feels oddly old-fashioned.

A series of loose skits, the film's humour is mostly below the belt, with an enormous number of jokes - a couple of them quite funny - about members, honourable and dishonourable. Cohen is a nimble physical comedian and some of the ripest sequences have him attempting hastily to turn a pratfall into a breakdancing routine, moonwalking across a booby-trapped room or applying cunnilingus to a canape at a posh reception.

The film's biggest departure from the TV shows is the way it tries to flesh out the character. We meet his nan, see him courting his girlfriend during his Goth period, find out that Ali is short for Alistair and realise in the process that he's less interesting than we originally thought.

Prod co: WT2
UK dist: UIP
Prods: Eric Fellner, Tim Bevan, Dan Mazer
Scr: Sacha Baron Cohen, Mazer
Dop: Ashley Rowe
Prod des: Grenville Homer
Ed: Paul Knight
Main cast: Sacha Baron Cohen, Michael Gambon, Charles Dance, Kellie Bright, Martin Freeman, Rhona Mitra, Barbara New