A Chinese court has sentenced a leading dissident to 11 years in jail for “inciting subversion of state power”, the clearest signal yet, according to analysts, foreign officials and human rights groups, that China has over the past two years reduced the already limited space for political dissent.

Although there were high hopes that events such as last year's Olympics in Beijing would encourage greater political openness in China, the unusually harsh sentence handed down to Liu Xiaobo on Christmas day has reinforced the impression that the more conservative voices in the Chinese leadership are in the ascendancy.

“The conviction and extremely harsh sentencing of Liu Xiaobo mark a further severe restriction on the scope of freedom of expression in China,” said Navi Pillay, UN high commissioner for human rights.

The charges against Mr Liu, 54, a former university professor who was also imprisoned after the 1989 Tiananmen Square protests, were based on six articles he published on the internet and his role in organising Charter 08, a petition which called for the end to one-party rule in China. He is to appeal against the sentence, his wife said at the weekend.

Legal experts said his sentence was the longest on record for “inciting subversion” since changes in the law in 1997.

The trial and swift conviction of Mr Liu have indicated that the more repressive political mood is not just a temporary phenomenon. “It seems that the more conservative, stability-above-all elements in the leadership have far more sway these days,” said Joshua Rosenzweig at the Dui Hua Foundation, which lobbies Beijing over political prisoners. “It is clear that this is not simply linked to certain sensitive events.”

He pointed to official figures showing a sharp increase in the number of arrests and convictions for “endangering state security” – these doubled in 2008 over 2007 and were nearly five times higher than in 2005.