You might expect a circus from Australia to begin with a man standing upside down. Tim Coldwell, a veteran clown and founder member of Circus Oz, emerges from a door and walks across the ceiling of the Royal Festival Hall to take a seat upside down in front of his dressing-room mirror, high above the audience. Maintaining the illusion that he is the right way up and it is the audience that is inverted, he travels head first down a pole towards the stage, heaving his body along with his arms in a perfect impersonation of a man ascending.

There is a world-weariness about our clown. He tells us that he's an old guy whose tricks meant something once, but no one wants to see them any more. "Oh yes we do!" the audience choruses, and the nice old fellow performs.

It is an early indication that, for all the joy and laughter we are about to experience, the circus from down under delivers us happiness with attitude. The audience may be filled with children, but politics lurks close to the surface of the show. A human cannon (renamed "humanitarian" for this circus) is wheeled on to the stage, to an accompaniment of gibes about weapons of mass destruction and Donald Rumsfeld. The human cannonball (Matt Wilson) has to fly over the "razor wire of oppression" and lands softly on a safety mat that has been carried on to the stage by members of the audience, and so is dubbed the "mat of human kindness".

During another of the acts, Coldwell takes the microphone to provide an un-usual backing track for a circus routine: a fast-moving impression of asinine debate in the Australian parliament. It satirises Canberra's support for the United States. I infer that Circus Oz is not a leading supporter of the campaign to re-elect John Howard as prime minister.

You get the impression of a tight-knit troupe that, despite huge respect for the tradition of circus, is determined to do and say its own thing in defiance of convention. It took me a while to realise that the panoply of acts - clowns, trapeze, juggling, bicycling and contortionism - is supplied by just 13 people, who also play the guitar, violin, drums and trumpet. The circus demands huge versatility from each performer: nearly every one of them is involved in hanging from a vertical pole at angles that require extraordinary strength and control. Virtually the whole troupe manages to clamber together on a single moving bicycle.

The circus was founded in 1977 with a stated commitment to "collective ownership and gender equity". Luckily, its philosophy also includes less pious qualities such as "a uniquely Australian signature" and irreverence. Presumably in support of the latter principles, the ensemble dress as cockatoos during the trapeze act, cawing loudly as they fly through the air, and depositing liberal quantities of droppings on to the stage.

The show has a strikingly orig-inal musical score, and the team is strong on humour and charisma. During the trapeze act, they sometimes miss their midair rendezvous and tumble on to the mats below. They simply get up and do it again. Sosina Wogayehu performs a beautiful juggling rou-tine, but occasionally the balls go off their own way. She just starts the trick over again.

One member of the troupe, Captain Frodo, maintains an amusing patter during a long but absorbing routine in which, dressed only in shorts, he contorts himself, manipulating his double joints and supposedly dislocating his limbs, in order to pass his entire body through two unstrung tennis rackets, one with a diameter of only 12 inches.

The sight of this young man stuck in hideous poses - one racket around his waist and thigh, forcing the leg uselessly into the air; the other around the shoulder that he was trying to dislocate; his arms scything the air as though disconnected - had the audi-ence squirming and cheering, wholly engrossed and thoroughly entertained, even though it was uncomfortably close to watching the flailing of someone with severe disabilities. In circus, because of its long heritage, we tolerate a level of political incorrectness that has been banished from other entertainment. To be sure, there are no animals these days, but we are still mesmerised by human bodies doing freaky and dangerous things, which seems worse.

It is also interesting that children, who experience such a range of diversions employing special effects, none the less understand the bounds of reality and appreciate it hugely when they see real people pushing themselves to the limits. There is no doubt that this show makes audiences happy, and they participate noisily. It is slick and full of the unexpected.

We could have got by with- out the last surprise. At the end of the show, after all the enthusiastic applause, Coldwell appeared gloomily on stage once more to tell us that the evening's performance had been dedicated to the principles of tolerance, diversity and human kindness. About half the audience cheered. Someone commented that the show was just too up itself. That came nearest to summarising my feelings, because Coldwell's post-curtain Antipodean moralising had left a strange taste in my mouth: something akin to cockatoo droppings, I suspect.