Mo Shaoping , a prominent lawyer who has defended several dissidents, said mainland lawyers faced many obstacles in the defence of their clients' interests and that conditions for criminal lawyers were the worst.

Mr Mo said lawyers had limited access to defendants, witnesses and investigation materials. Only 30 per cent of accused criminals were represented by a lawyer, with the rate falling to as low as 10 per cent in some regions.

The procedure law states that lawyers should be able to meet suspects within 48 hours of being arrested. But in practice, authorities can prevent those meetings, delaying contact with clients for months. Even when lawyers and clients do meet, police sometimes sit in on the meetings or even stop them.

'If suspects cannot meet lawyers in time, the police may make use of the fragile state of the detainee to coerce or threaten suspects, or even extract a confession by force,' Mr Mo said.

He said more lawyers were giving up criminal law because of the difficulties and the occasional risks.

Mr Mo said lawyers faced up to seven years in jail if a court convicted them of perjury in the defence of a case, a situation that could arise if a prosecution witness recanted a statement in favour of the defendant. About 300 lawyers have been charged with perjury since the offence was put on the books in 1997.

A series of high-profile reports has also exposed police wrongdoing in investigations and highlighted the need for lawyers to have access to witnesses.

In one case, Hebei farmer She Xianglin spent 11 years in jail after police tortured him into confessing to killing his wife, who later turned up alive. And last year authorities discovered they had wrongly executed Hebei man Nie Shubin 10 years ago for rape and murder.

Mr Mo said witnesses had to help police in their investigations but were under no legal obligation to give statements to lawyers.

He said that in more than 90 per cent of cases, witnesses were not present in court and prosecutors needed only to submit witness statements in favour of their case.

'Lawyers and procurators are not on the same footing,' Mr Mo said. 'But a criminal defence is a human right.'

Pu Zhiqiang , who represents clients mainly in civil and administrative cases, said advocates in his area of the law had similar problems getting access to dossiers, but the semi-official lawyers' association was also causing difficulties in their work.

Earlier this year, the All-China Lawyers Association issued a directive requiring lawyers to report to government if they received any information on mass incidents such as demolitions and relocations, pollution and unemployment.

The directive also put controls on lawyers' contacts with the media, particularly overseas media. 'Clients have to take the consequences of restrictions on lawyers' rights. Restricting a lawyer's rights means violating citizens' basic rights,' Mr Pu said.

Last month, Shanghai-based lawyer Zheng Enchong was released after serving three years in jail for leaking state secrets to an overseas human rights group about labour and property disputes.