“Heeeerre’s Brüno!” screamed the MC, and he appeared to the sound of trumpets, like Spartacus.

In this case, the trumpets played I Will Survive and the conquering hero led a phalanx of muscular black men dressed as the guardsmen of Buckingham Palace. But there was no doubt that he had conquered and survived.

Sacha Baron Cohen’s flamboyant gay Austrian fashion journalist had visited a refugee camp in Lebanon and told a leader of al-Aqsa Martyrs’ Brigades that Osama bin Laden resembled a homeless Santa Claus.

At a cage fight in darkest Arkansas, he had stripped to his underwear and kissed his erstwhile opponent in front of a drunk and angry mob. At a swingers’ party he had stood in his underpants before an increasingly irate dominatrix and asked her to wear a beard.

He had done all this and lived to tell the tale, and now he pranced proudly into Leicester Square, the soldier of British satire, followed by his mock guardsmen. All wore red coats without sleaves and black leather hot pants.

Some also wore a slightly bemused expression, as if reflecting on the things that they did for money. Only Baron Cohen looked truly comfortable, dressed as Brüno, the lead in the crazed “mockumentary” that had its premiere last night. “This is the most important film starring a gay actor since Terminator 2!” he shouted.

The crowd also seemed very slightly uneasy, as if uncertain what he might do while in character. For Baron Cohen is the modern incarnation of the court jester: once in costume, he will say and do anything. First as the wannabe gangster Ali G and then as Borat, the anti-Semitic Kazakh broadcaster, he has made his fortune by doing so in increasingly awkward situations while the cameras roll.

Brüno pushes things further and harder, as it were, than either of those characters. There are not many places where his creations can survive unrecognised for the shams they are, and to judge by the film, those places are Jerusalem, Lebanon, a few suburbs in Los Angeles, the training base of the American National Guard and the states of Arkansas and Alabama.

A threadbare plot takes him to each in turn. After donning a velcro suit to cover a fashion show, Brüno becomes attached to parts of the set and invades the catwalk wrapped in a curtain: for this outrage he loses his position as a TV host. Concluding that the fashion world is shallow and self-serving, he abandons it and sets off for America hoping to become a celebrity.

The scenes that follow are unpredictable and occasionally extremely funny. The terrorist leader, the Republican Congressman Ron Paul, the Americans on a hunting expedition who will not let him into his tent despite his claims that a bear has eaten his clothes and left him naked but for a packet of condoms: all display the required quotient of homophobia that the film sets out to expose.

Sometimes this works, sometimes it can feel rather tiresome. It would have been more interesting to uncover latent homophobia somewhere closer to home than Arkansas, but perhaps less entertaining for Baron Cohen’s staple audience. In any case that option is of course no longer open.

The gay community has debated whether Brüno satirises homophobia or reinforces stereotypes, though this almost seems to be beside the point. Fans will see the film for the unrelenting foolery he promises, and delivers, with strange people in strange places.

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