It works particularly well on people who have some degree of psychological sophistication

Dr Kishore Chandiramani

His work also showed that inmates who studied the technique were less prone to depression, feelings of hostility and helplessness and a sense of hopelessness.

They were also less likely to smoke.

The prisoners themselves readily accepted the technique, said Dr Chandiramani, and the cost of running training courses was minimal.

In addition to prisoners, several hundred police officers and prison staff voluntarily learned the technique for their personal development.

A separate study, by the National Institute of Health in the US, is examining the impact on prisoners' wellbeing.

However, staff at a prison in Seattle have reported that the technique lead to a reduction in inmate drug and alcohol addictions among inmates.

Dr Chandiramani told BBC News Online that in two Indian prisons where the technique had been taught separate wards set aside for troublemakers were now largely empty, whereas previously they had always been full.

Very intensive

He said: "This technique is a very intensive form of meditation and works at an unconscious level.

"It works particularly well on people who have some degree of psychological sophistication.

"However, it is unlikely to work for people who are so restless, or agitated that they cannot understand and follow the instructions."

Dr Chandiramani said about a third of prisoners had very significant psychiatric problems, but that many prisons did not have sufficient resources to offer patients access to psychiatric services.

There was also a danger that inmates would become addicted to psychiatric medications.

He said Vipassana Meditation offered a cheap, practical alternative.

"The technique should be tried on an experimental basis, to see if prison staff are happy with it."

Ancient technique

Vipassana, which means to see things as they really are, is one of India's most ancient techniques of meditation.

It was taught in India more than 2,500 years ago as a universal remedy for universal ills.

The technique is designed to improve self-awareness by focusing on the connection between mind and body.

It is taught on a 10-day residential course, for a large part of which the students are totally silent.

Students learn how to divorce themselves from the past and future, and how to concentrate exclusively on the present.

The research was presented at the Royal College of Psychiatrists annual conference in London.