Lam pleaded guilty in September last year to one count of misconduct in public office for inducing patients to make donations and payments of almost HK$4 million to his company.

A person close to Lam said: 'He was never prepared to be jailed. It was a big shock to him when he learned about the sentence.

'He had told his patients before the sentencing that he would be only away for a short while before going back to the clinic.'

One doctor said: 'It [the release] sounds too early. It may send a wrong message to the public that his crime is very light.' But another doctor said the system was fair. 'The correctional system is designed for all ... all people have the same chance for this early release scheme.'

In theory, Lam can still practise after his release. He is required to secure employment for the supervision period under the pre-release employment scheme.

Medical Council member Dr Choi Kin said the watchdog would hold an inquiry into any doctor convicted of a criminal offence to decide if the doctor could continue to practise. Before an inquiry is held, a doctor can still practise.

A Security Bureau spokesman said yesterday the early release scheme allowed 'eligible prisoners to serve part of their sentence in an open environment under the supervision of correctional officers so as to facilitate their early reintegration into society and lead a law-abiding life'.

The scheme had been successful, as none of those who joined it between 2007 and 2009 had re-offended, he added.

Under prison rules, prisoners with good disciplinary records can be granted remission of up to a third of their sentences.

For example, the spokesman said a prisoner sentenced to 24 months imprisonment would be eligible for release after serving 16 months, with remission. If the prisoner successfully applied for the pre-release scheme, he could be transferred as early as 10 months after serving his sentence in prison to a correctional services hostel. There, he would complete the remaining six months of his sentence. The Release Under Supervision Board received 256 applications for the pre-release employment scheme between 2007 and 2009. Fifty-seven per cent of the cases, or 147, were approved.

General secretary of the Hong Kong Christian Kun Sun Association, the Reverend John Pun, said the scheme was good for rehabilitation. Usually, a first offender who was stable and behaved well in prison could apply for early release.

'Those who are released early under supervision in this scheme are required to live in a hostel. They need approval if they want to go back home on holiday,' Pun said. Early-release prisoners should earn a living on their own under the guidance of the supervising officers, he said.

Correctional services officers familiar with the situation said Lam had been jailed in Ma Hang Prison, an institution used mainly for elderly inmates.

He had been very quiet in his cell and stayed in the sick bay most of the time during his sentence, as he applied for medical treatment for a chronic disease, the officer said. He did not have details of the disease.

He read medical books most of the time he was in the prison, the officer added.

Who's eligible to get out early?

What kind of inmates are eligible for the pre-release employment scheme?

- those serving a sentence of 2 years or more and;

- are within 6 months of their earliest date of discharge and;

- have secured employment for the supervision period and;

- will stay in a hostel managed by the Correctional Services Department during the supervision period.

Source: Report of the Release Under Supervision Board