British psychiatrists are beginning to debate the highly sensitive issue of using LSD for therapeutic purposes to unlock secrets buried in the unconscious which may underlie the anxious or obsessional behaviour of some of their patients.

The UK pioneered this use of LSD in the 1950s. But psychiatrists found their research proposals rejected and their work dismissed once "acid" hit the streets in the mid-60s and uncontrolled use of the hallucinogenic drug became a social phenomenon.

Today, on the 100th birthday of Albert Hofmann, the scientist who discovered the mind-expanding properties of lysergic acid diethylamide in Switzerland, one consultant psychiatrist is openly risking controversy to urge that the debate on the therapeutic potential of LSD be reopened. Ben Sessa has been invited to give a presentation on psychedelic drugs to the Royal College of Psychiatrists in March - the first time the subject will have been discussed by the institution in 30 years.

"I really want to present a dispassionate medical, scientific evidence-based argument," says Dr Sessa. "I do not condone recreational drug use. None of this is tinged by any personal experience.

"Scientists, psychiatrists and psychologists were forced to give up their studies for socio-political reasons. That's what really drives me."

LSD was brought to the UK in 1952 by psychiatrist Ronnie Sandison who had visited the labs of the drug company Sandoz, where Dr Hofmann worked. He came home with 100 ampoules in his bag and began to use them at Powick hospital, near Malvern in Worcestershire, on selected patients with conditions such as obsessional hand-washing or anxiety who did not respond to psychoanalysis.

Dr Sessa has looked back on the papers published by Dr Sandison and others from the heyday of psychedelic psychiatry, and thinks they may have modern relevance. They claim positive results in patients who were given LSD in psychotherapy to get to the deep-seated roots of anxiety disorders and neuroses. It took them, as the title of Aldous Huxley's book has it, from the poem of William Blake, through "the doors of perception". Yet when he was a student, says 33-year-old Dr Sessa, all his textbooks stated categorically that LSD had no medical use.

"It is as if a whole generation of psychiatrists have had this systematically erased from their education," he says. "But for the generation who trained in the 50s and 60s, this really was going to be the next big thing. Thousands of books and papers were written, but then it all went silent. My generation has never heard of it. It's almost as if there has been an active demonisation."

He says he understands why. LSD became a huge social issue. But he argues that nobody would ask anaesthetists to forgo morphine use because heroin is a social evil, and cannabis is now being formulated as a therapeutic drug.

Since the 1960s, when research was stopped on LSD, "depression and anxiety disorders have risen to almost epidemic proportions and are now the greatest single burden on today's health services. Therefore, today's political climate may be just right for the medical profession to reconsider the use of psychedelic drugs", writes Dr Sessa in an as-yet unpublished paper with Amanda Feilding of the Beckley Foundation which promotes research into the nature of consciousness.

A major conference is being held in Basel, Switzerland, this weekend in honour of Dr Hofmann's birthday. Scientists in the burgeoning psychedelic psychiatry movement will be there, alongside artists, musicians and those who look to hallucinatory drugs for spiritual experience.

In the past five years, the international climate has been changing, albeit very slowly. In the US, Israel, Switzerland and Spain, a few research projects have been permitted into the effects of LSD, MDMA (ecstasy) and psilocybin - the active ingredient in magic mushrooms - on the brain. They look at the use of the drugs in conditions such as post-traumatic stress, obsessive compulsive disorder and the alleviation of distress in the dying.

But Dr Sessa knows it will be an uphill struggle to get research proposals approved and funded in the UK. He believes the drugs are safe in medical use - given in a pure form in tiny doses and in controlled and supervised surroundings. But LSD is associated with flashbacks, and brain scans of clubbers using ecstasy have shown damage. Some psychiatrists are likely to be appalled at the idea. Former patients of Dr Sandison claimed his use of LSD had caused them long-term problems and attempted to bring a court action for compensation.

Dr Sandison says his early experimentation with LSD in the 50s produced results in difficult cases. "I recall one young woman. She had a near-drowning experience. She developed a severe anxiety state. It coloured everything.

"We didn't get anywhere with ordinary psychotherapy, so we went on to LSD. She recalled an extraordinary memory of how, when she was eight, she had gone into a store with her mother and become separated from her. She went to a counter to ask an assistant and felt a man behind her trying to feel her up. She felt very confused by this and said she thought it was an odd way of stealing her purse." he said.

"It was pretty alarming. She had suppressed all this. We began to get somewhere and we discovered why she had sexual difficulties with her husband and felt angry towards men."

In 1954 he wrote his first paper, for the Journal of Mental Sciences, on LSD use in 36 patients. It concluded: "We consider that the drug will find a significant place in the treatment of the psychoneuroses and allied mental illnesses." But by the mid-60s, Dr Sandison had had enough. The drug had become a street problem. He gave evidence in a couple of Old Bailey cases where arson and a murder were committed under the influence of LSD.

"I don't see either ethically or professionally or technically why it shouldn't be used in the future," he says. "But anything done now has to be very different from what we did. All the expertise developed in those years by a large number of people has been lost so we have to start again."