Ai Weiwei's detention is part of a worrying trend in China

CELEBRITY offers no protection from the vengeful arm of the Chinese state. On the contrary, that the artist Ai Weiwei was perhaps the most famous of the Chinese Communist Party's domestic critics still at large rendered his liberty more precarious. As the most extensive round-up of dissidents for years spread its dragnet, Mr Ai was always likely to find himself in its folds.

He was detained at Beijing airport as he tried to board a flight to Hong Kong, perhaps to attend art auctions. His travel companion was allowed on the plane, and told that Mr Ai had “other business”. That was on Sunday morning. By Monday evening, nothing had been heard of him.

As the son of a revered poet, Mr Ai comes from the Communist Party's equivalent of the aristocracy. Besides being China's best-known artist, with an installation now on display at the Tate Modern gallery in London, and a lasting legacy in the shape of the “bird's nest” stadium in Beijing built for the 2008 Olympics, Mr Ai was one of its most trenchant dissidents. He pulled few punches, as can be seen in an interview on this website, in which he said he had totally lost hope in the current government, and suggested that young Chinese should learn English and emigrate.

Mr Ai has been in trouble before. Last year he was prevented from travelling abroad—apparently to ensure he could not attend the ceremony in Oslo where Liu Xiaobo, a jailed Chinese dissident, was awarded the Nobel peace prize. He was briefly put under de facto house arrest. This January his studio in Shanghai was demolished, an act Mr Ai saw as retribution for his political activism.

This time, the authorities seem determined to find evidence of some “crime”. At noon, about two hours after his detention, a dozen police officers arrived at his studio. They questioned the seven or eight people they found there, detained them all day, and confiscated at least 13 computers and one notebook. Freed from detention, but shaken by the experience, Mr Ai's associates feared the worst, thinking that this time Mr Ai's troubles are more serious, and that the instructions to take action against him have come “from the top”.

This forms part of an intensifying repression of the party's opponents and critics, in large measure a response to the “jasmine revolutions” in the Middle East and north Africa, and incipient internet campaigns to emulate them in China.

The online activism has inspired the government to tighten internet censorship, force some liberal newspaper editors to step down and impose tight restrictions on foreign reporters in China. According to Human Rights Watch, an NGO, it has also led to the most severe crackdown on dissent in a decade. It reports that, since mid-February, up to 25 lawyers, activists and bloggers have been detained or arrested by state authorities, or have vanished in unexplained circumstances.

It also reports that “between 100 and 200 other people have been subjected to an array of repressive measures ranging from police summonses to house arrest.”

There are two worrying features to all this. One is the use of the law to impose political orthodoxy. On March 25th Liu Xianbin, an activist, was sentenced to ten years in prison for “slandering the Communist Party”. But second is the increasingly common resort to informal detentions, punishments and disappearances which are completely outside the law, and so offer the government deniability and the victim no protection whatsoever.

The government now dismisses the idea that one function of the law is to defend people against the arbitrary exercise of state power. On March 4th a Chinese foreign ministry spokeswoman told foreign journalists who had been beaten up by Chinese police while going about their work: “Don't use the law as a shield.” Some people, she said, want to make trouble in China and “for people with these kinds of motives, I think no law can protect them.”

Celebrity may at least help Ai Weiwei avoid vanishing for too long into this legal black hole. But it will do little to shield him from the wrath of China's vindictive rulers.