But his ruling means that all the evidence in the trial will be heard in secret, despite having earlier invoked the sections of the law that have always been used to protect the identity of victims in such cases.

The decision angered legal and constitutional experts who feel that the basic principle of open justice is being increasingly eroded by judges.

In this case even the not-guilty pleas entered by the defendant to two charges of incest were heard in camera, although it is expected the verdict will be given in open court.

The controversial ruling was made when the judge granted a prosecution application, supported by the defence, that such a course be taken.

Judge McMahon, formerly a leading prosecutor in the Legal Department, said: 'It is in the interests of the public and the interests of justice.

'I have taken into consideration that trials in Hong Kong should be as open as possible.' But a senior lecturer in law at Hong Kong University said the judge was setting a dangerous precedent.

Dr Nihal Jayawickrama said: 'This suggests that all incest cases should be held in secret and that is totally unacceptable.

'The principle of law established by the Bill of Rights is that all hearings shall be heard in public.' He said if the judge had to conduct justice behind closed doors he should have done so for only part of the case, which he can do under the Bill of Rights.

A leading constitutional expert, who did not wish to be named, said: 'It is appalling and utterly wrong. This is a significant intrusion into well-established constitutional rights.

'It bodes very badly for the future and will make people even more conscious of 1997.' The ruling raises important questions about open justice in Hong Kong. The public will not be able to hear the girl making her allegations or her father defending the charges.

Legal sources say concern for the well-being of a young witness is understandable. But they point out that other witnesses in sex cases, many of them much younger than the girl involved in this trial, give evidence in open court.

The judge refused to allow a member of the press to address him on the matter.

He then cleared the court of press and public.

A sign reading 'Court in camera - no admittance' was placed on the door.

It was only after this that the defendant, 44, pleaded not guilty to two charges of incest, first when his daughter was 15 and then when she was 17.

The judge ordered that nothing should be published that would lead to the identity of the girl being revealed.

The trial began with the alleged victim giving evidence.

Afterwards prosecutor Pamela Cheng said she applied for the 'in camera' order for the well-being of the witness and because of the nature of the evidence.

'She is a blind girl. We want justice to be done. We have to take care of her,' she added.

Judge McMahon made his order under Section 123 of the Criminal Procedure Ordinance.

This allows for a trial to be held behind closed doors if the court is satisfied it is for the well-being of a witness or if a witness is apprehensive about what may happen to him or her as a result of giving evidence.

The judge's ruling comes less than five months after the storm surrounding a decision by Deputy Judge Nigel Jones to pass sentence on a drug trafficker when the court was in camera.

Judge Jones later admitted he had been wrong.