A shift to the left?

New details have emerged in Shanghai of the Communist party's most significant purge of the past decade in an unfolding power struggle over the future of the Chinese economy.

The political upheaval deepened this weekend with a round-up of businessmen and lower-ranking officials by secret police and every Shanghai official above the rank of office director has had to surrender his passport.

It is Communist China's first purge in the internet age, allowing Chinese analysts an opportunity to examine how the party has used both cyber-propaganda and old-fashioned repression against its victims.

They have vanished into a labyrinth of well-guarded villas where they are being questioned by party interrogators under draconian internal disciplinary procedures that give the accused no legal rights.

The purge is seen as a decisive move by President Hu Jintao to cement his authority and to satisfy demands from the left to restrain China's freewheeling brand of capitalism.

Local journalists who have followed the dramatic events of the past week say the president's men updated their traditional methods by orchestrating an online campaign against the Shanghai party chief, Chen Liangyu.

It began last Monday, when the state news agency, Xinhua, revealed that Chen had been sacked for alleged corruption over a scandal in which at least £215m, a gigantic sum by Chinese standards, had been either unwisely invested or misappropriated from the city's pension fund.

Upon news of Chen's downfall, the party's cyber-tacticians sprang into action as more than 300,000 readers logged on to the Xinhua website within half an hour to read the charges. On cue, thousands of internet users were encouraged to write comments applauding the government for acting against corruption.

Chatroom censors blocked anything sceptical. Internet users suspected that state security agents were planting well-timed messages to steer the chat in the correct direction. They did not neglect the Shanghai city website, from which all portraits and speeches by Chen, who studied at Birmingham University for a few months in 1992, vanished at the click of a mouse.

At the same time, the party's well-worn techniques of detention and denunciation were brought into play. Plainclothes agents, accompanied by officers from the Public Security Bureau wearing olive green uniforms, ushered those under suspicion from their grandiose offices into black limousines that sped them to secure locations around the city...

To some analysts, this dramatic return to the days of detentions and purges is merely a powerplay by Hu ahead of a central committee meeting next month and a big party congress next year. To others it means the president has struck an alliance with the old guard, whose doctrines of state control have been reasserted in a stream of recent edicts.

If that is the case, then the purge in Shanghai heralds a fundamental shift back to the left in China.