Ali G doesn't as much attack every sacred cow as drop them onto the Staines bypass from the nearest pedestrian bridge. During rush hour.

This is foul-mouthed, puerile, sometimes insulting, often immature, always toe-curlingly crass and, for much of the time, pretty good fun.

You have to laugh in spite of yourself or you would buckle under the relentless barrage of gags that writers Baron Cohen and Dan Mazer have put together.

The modus operandi is quite simple - if you don't like one joke, there'll be another one along in a nanosecond that you will. It's called the scattergun approach.

There's not a lot of point bothering with the plot but here goes, anyway.

Ali (Baron Cohen) is recruited by conniving deputy prime minister Carlton (Charles Dance) to run as MP for Staines.

Surprisingly, after revealing the Tory opposition's unhealthy obsession with a horse, he wins and finds himself courted by Prime Minister Michael Gambon for the youth vote.

Bizarrely, Ali's alternative manifesto, which includes smoking as much marijuana as is humanly possible, proves a vote winner and soon the party is riding high in the polls.

All this is bad news for Carlton, who thought the PM would be tainted by his association with Ali, leaving the door open to the leadership for his good self. So he has to think again.

Of course, the plot doesn't really matter, and merely acts as a platform from which Ali can have a pop at everyone from wannabe gangstas to self-serving politicians.

What lifts this above the normal, common-or-garden gross-out comedy is the character that Baron Cohen has created in Ali G.

Originally a bit player in television's 11 O'Clock Show, he used the opportunity to prick the pomposity of those in power in a series of spoof interviews.

Here he targets the corrupt Tory regime which predated Tony Blair's New Labour but - to be brutally honest - he's about five years too late.

Ali is on firmer ground when he's parodying the risible 'respect' culture of youths who are under the impression their 'hood is South Central LA when in fact they live in, well, Staines.

Also into the satirical mix is thrown the gangsta culture's neanderthal attitudes to gays and women (Ali's windscreen shade reads "Ali" and "Me Bitch").

The Daily Mail has called this "the most obnoxious British film ever". No, it's not. It's just a film.

Tim Evans