Borat is Kazakhstan’s one and only international celebrity and the government of the Central Asian republic is furious about the fact. The tactless television reporter has turned the country into a fabulous joke. Borat is the proud ambassador of a nation stuck in the Monty Python Middle Ages. His politics are medieval; his honesty is magnetic. He is a vain and unreconstructed racist with a dotty grip on modern life. His Quixotic mission is to unlock the secrets of American culture for the benefit of jealous peasants in Kazakhstan. But the campaign is doomed before it starts.

Borat’s surreal exploits have made newspaper headlines. His media stunts have launched a thousand websites. The powers-that-be in Kazakhstan are aghast because the global profile of the country has been hijacked by a clown. The irony, of course, is that Borat is a total fiction, and British to boot. He was a shallow character invented and played by Sacha Baron Cohen during his Ali G days to skewer pompous English gits.

Larry Charles's big-screen account of Borat's cockeyed adventures is a squirming joy and a film to cherish. It begins in a muddy village in Kazakhstan. This, explains Borat, is home. He is a cool and confident narrator. He introduces neighbours and hugs the local rapists, criminals and psychopaths. There is a cow in his state-of-the-art living room. This is rural bliss. Women are inherently stupid; incest is normal; bestiality is best. It’s a civic duty to butcher gypsies and Jews. It’s good, clean, normal fun.

The satire of Charles's faux documentary lifts off when Borat arrives in New York sporting a cheap, shiny suit and a preposterous accent. He has a live chicken in his luggage. He tries to be cosmopolitan but he is constantly stumped by strangers in the street who flinch from his kisses or threaten to rearrange his jaw. But his exotic credentials open surprising doors. He is interviewed by local news channels, invited to worthy events and told to shave off his moustache in case he is mistaken for a suicide bomber.

In 81 hysterical minutes Borat destroys the myth of an open-minded society. Hardcore feminists walk out of the room when he tries to find out if they are actually female. There are wild cheers at a Texas rodeo when he shouts “George Bush drinks the blood of every man, woman, and child”.

Sacha Baron Cohen is so reckless and relaxed in the role that you fear for his safety. His curiosity excites the most patronising sympathy. He is invited to a pompous supper with experts in table manners. His barnyard manners inspire polite horror, and then complete outrage when a black prostitute suddenly turns up as his last-minute guest.

Borat’s zealous admiration of western values is forever spiked by his complete failure to absorb a single one. He does try. He falls head over heels for Pamela Anderson after watching an episode of Baywatch in his hotel room. He races across America in an ice-cream van in the sincere belief that he will marry her, but his disillusion in the topsy-turvy values of the free world ultimately makes him resort to brute Kazakhstan type.

The best moments of Borat are improvised and impulsive - such as the New York street scenes - but it's the satire that really stings.