The door of the bus closed before Mr Yan could get off. He called out to the driver several times to stop and let him off, but his pleas were of no avail.

An argument ensued, during which Mr Yan, in his late 40s, says he accidentally knocked over the ticket collector's folder of tickets and money.

''There is 1,000 yuan [HK$1,340] there, and you must compensate for every cent lost,'' the conductor yelled. Mr Yan, who did not touch the money, tried to get off at the next stop, but was prevented from doing so.

When the bus arrived at the Summer Palace, Mr Yan, to his surprise, was met by three policemen carrying electric batons. One of them grabbed Mr Yan's hair, another slapped his face and the third struck him with an electric baton.

They pushed Mr Yan off the bus, knocked him to the ground with the baton then took him to the police station.

''They handcuffed me very tightly, and after only a few minutes, my hands became the colour of pig livers and ached,'' Mr Yan said in an interview published in a Chinese newspaper. ''I told them: 'I am an NPC member, and it is illegal to handcuff me.' '' The policemen beat him even harder.

''What if you are an NPC member?'' Mr Yan quoted one of the policemen as saying. ''Even if you were a premier, I would deal with you. I want to deal with exactly your sort.'' MR YAN said he was then beaten dozens of times, in his groin and stomach and elsewhere. One of his teeth was knocked out. One policeman threatened to beat him to death.

''Help, the police are beating me,'' Mr Yan cried. In the quiet night, his screams were apparently heard by many residents, winning a half-hour reprieve from the beating.

A senior officer came along, questioned Mr Yan, took some notes, and then the three policemen kicked the artist as they forced him out of the station.

Later, Mr Yan took his complaint to a police inspection department, where he was told he should have taken out his NPC identification card and shown it to police for protection, as parliamentary delegates are immune from police prosecution.

The inspection department's response was absurd. ''Though I'm protected by the law, even I don't have a chance to exonerate myself, and am beaten up so brutally. What about common people?'' he said.

Much worse things happen to ordinary Chinese.

Despite the propaganda which normally casts the police force as the brave protectors of the common man, public security is earning a reputation for brutality and corruption.

To cite one of dozens of examples reported in the official press, in rural Shanxi province recently, the son of a senior police officer in Linxi county quarrelled with a peasant after running his motorcycle through a market and knocking over the peasant's vegetable stand.

The young man's father used his power to arrest the peasant and the peasant's son. Police beat them both, and the son died.

It was not until the provincial governor intervened that the case was resolved, with the officer getting three years in jail and two policemen being sentenced to death.

No wonder the vice-minister of Public Security, Jiang Xianjin, recently admitted the image of police had become seriously tarnished, and that relations between the police and the masses had been damaged.

In Mr Yan's case, Public Security offered as settlement of the case personal apologies from the offending policemen. But Mr Yan has decided to sue.

''What I want to tell people is: even rubbish collectors should not be treated like this. It is inhumane,'' he said.