In a sign of Beijing's renewed hard line against dissent, a Chinese activist has been jailed for five years after he investigated whether shoddy construction contributed to deaths of thousands of schoolchildren in the devastating 2008 earthquake.

The charges against Tan Zuoren, 55, a longtime activist in southwestern Sichuan province, involved “inciting subversion of state power” because of essays in which he criticized the bloody crackdown against pro-democracy demonstrators in Tiananmen Square on June 4, 1989.

But friends and his lawyers were in little doubt that Mr Tan’s efforts to document and produce an independent report on the collapse of school buildings in the Sichuan earthquake in May 2008, when some 90,000 people died, were behind the sentence.

His lawyer, Pu Zhiqiang, told The Times: “The court can do whatever it likes. His crime was inciting subversion of the state, but they did not have a scrap of evidence. In fact Tan Zuoren had only voiced differing views about June 4 and written some essays over the course of 20 years. After 20 years he is to go to jail. This is tragic and a cause of much anger.”

Mr Pu said: “The court is violating the constitution since Tan Zuoren was merely exercising his right to freedom of speech.”

Mr Tan had been put on trial in the provincial capital, Chengdu, last August. In China, most verdicts are announced within hours or days of the trial, but in this case the court waited until the final day of the legally stipulated period before passing sentence.

The sentence against Mr Tan was the maximum possible for his crime. The severity of the term highlighted the increasingly tough approach adopted by the Government in recent months against any hint of dissent.

Leading dissident Liu Xiaobo was jailed for 11 years in December for subversion – the harshest sentence ever handed down since the charge was introduced in 1997.

It took the court just 10 minutes to read out the verdict against Mr Tan. His lawyer said: “There were no charges related to the quake. All of the proceedings were linked to June 4 (1989)."

Mr Tan was the first person in a decade to be sentenced for actions linked to the 1989 crackdown. Most supporters and human rights activists were in little doubt that it was his attempts to document whether schools had been built on the cheap and were thus particularly vulnerable when the earthquake hit that had angered the authorities.

His wife, Wang Qinghua, told The Times she had been prevented from entering the court to hear the verdict.

“I was mentally prepared for such a long sentence and we will appeal. I understand that my husband tried to make a statement but he was not allowed to finish,” she said.

Ai Weiwei, a prominent and outspoken artist who helped to design the Bird’s Nest stadium for the Beijing Olympics and had also campaigned for a full accounting for child victims of the earthquake, said the case was a travesty of justice.

He said: "I think this is a very important case for China, more important than that of Liu Xiaobo. It shows the Chinese legal system has taken a big step backwards. Tan's 'crime' was entirely one of speech, of conscience."

Last year, a court in Chengdu sentenced activist Huang Qi to three years for “revealing state secrets” after he tried to gather information on faulty construction of school buildings that critics say contributed to the children’s deaths. More than 5,000 of the dead were children.

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