#aiww: The Arrest of Ai Weiwei, Hampstead Theatre

During rehearsals of his new play, Howard Brenton and the company had a sudden realisation: they were willing partners in "the vast Ai Weiwei project". The Chinese dissident artist, a constant critic of his country's human rights policies, was arrested on his way to Hong Kong in 2011 because his travel would "damage state security" and detained for 81 days. Now he requested that this story be told in a play to be based on interviews he had given to the journalist Barnaby Martin.

One of the conditions for his release had been that he should not speak to foreign journalists. And here he was seeking a wider audience for material already published in Martin's book, Hanging Man. Brenton, who has visited China several times, has observed that Ai Weiwei is clearly putting himself in further danger.

Brenton, returning to a contemporary political subject after his forays into history with Anne Boleyn and the exploration of Charles I's trial, 55 Days, has kept closely to Martin's account of the artist's detention and interrogation. He has added only two wholly imagined scenes between senior officials as they discuss their high profile prisoner's fate. 

Although there is the considerable tension of a story still dangerous, still unfinished, the overall effect is matter-of-fact

Ai Weiwei's treatment seems to have been bizarre rather than brutal, terrifying more for what might have happened than for what actually did. He confidently expected to be beaten and knew that there was every chance he might simply disappear for good. In the event, he was guarded for some time by a couple of bored young country boys and first questioned by a police department specialising in murder investigation. Later he was placed under military guard and forced to follow a mindlessly disciplined regime, sleeping on demand and being observed every second, including in the lavatory. By the end, surprisingly, his captors were discussing Dada and Duchamp with him. 

Ai Weiwei's release came suddenly after he agreed to accept the false accusation that he was guilty of tax fraud. Brenton has imagined that officials began to think, in the light of criticism especially from foreign governments, that an imprisoned Ai Weiwei might be the equivalent of his most outspoken artwork. While Brenton has taken pains to show representatives of the Communist state as men of some sophistication and culture, running through the play is a complete bemusement about art movements in the past century. Ai Weiwei's 100 million clay sunflower seeds - all the same, yet each subtly different - which was such a popular exhibit at Tate Modern, his installations featuring bicycles and chairs, and his satirically humorous photographs are assumed to be anti-Communist. Yet Ai Weiwei designed the spectacular "Bird's Nest" for the 2008 Beijing Olympics and only fell foul of the authorities when he subsequently criticised the Games.

The interrogation scenes do not have the intensity of, say, a verbatim tribunal. Although there is the considerable tension of a story still dangerous, still unfinished, the overall effect is matter-of-fact, deliberately kept low key by James Macdonald's direction which requires all the cast to be onstage throughout, assembling sets as needed. Ashley Martin Davis's design has a cube at its centre made of scenery flats which open out to reveal cells. The effect is of a series of installations featuring Ai Weiwei's story; for once this artist, known for commenting on the world beyond the individual, is himself at the heart of his art. Benedict Wong inhabits him - his courage, his circumspection, his unfettered imagination - so completely that it is hard not to believe one has been in the company of the man himself.

Ai Weiwei's contention, that it isn't the art itself that matters, but its effect, could scarcely be more relevant than it is here. This is not Howard Brenton's most exciting play, but its subject may well be the most important he has tackled and its consequences far-reaching.

A fierce advocate of free expression, Ai Weiwei became known internationally for his blog until the authorities closed it down. Twitter is harder to control: hence the title, a real twitter account. The play is destined to reach an audience way beyond Hampstead when it is streamed live for free tomorrow night.

• #aiww at the Hampstead Theatre until 18 May