In 1975 the release of One Flew Over the Cuckoo's Nest - in which the hero, played by Jack Nicholson, is reduced to a smiling zombie by electro-convulsive therapy and a lobotomy - dealt a severe blow to the reputation of the psychiatric profession.

The film won five major Oscars, and the treatments it showcased won instant notoriety as relics of a cruder and crueller age of medicine: clumsy tools abused by pitiless staff to suppress free will and individuality.

You might think, almost 25 years later and in the age of super-smart drugs, that such procedures had long been consigned to the history books, but you'd be wrong. Last week it was revealed that British doctors supervise 1,300 ECT treatments each week. Most of these patients are women and many are treated without their consent.

Then, at the weekend, it emerged that Lena Zavaroni, the former child star, had died after "pioneering surgery to cure her chronic anorexia". Newspaper reports described "a leucotomy" and "stereotactic surgery", but these are both terms for what is essentially the same operation: a lobotomy. In the bad old days, a lobotomy involved surgeons opening up the skull, having a poke around and then effectively destroying parts of the frontal lobe of the brain by hacking through the bundles of fibres which attach it to the rest of the brain - although it is this frontal lobe which makes us characteristically human.

Psychosurgery has probably been around for more than 40,000 years - neolithic skeletons have been found with holes drilled in the skulls. However, it was only in the last years of the 19th century that it acquired a scientific gloss. In 1894, a Swiss surgeon experimented by selectively destroying parts of the frontal lobes of several patients in a bid to help control their psychotic symptoms. He knew from cases involving patients whose frontal lobes had been damaged in accidents or by tumours that this part of the brain has a profound influence upon human emotions.

A Portuguese neurologist, Dr Antnio Egas Moniz, then refined the technique. His results were considered so good that lobotomies started to be used in several countries as a last-ditch treatment for psychosis or severe depression. Moniz was awarded a Nobel in 1949.

Two American surgeons went on to develop a quick and easy version which could be performed in just a few minutes under local anaesthetic. This involved the insertion, with one slight hammer blow, of an ice-pick instrument through the front of the skull followed by a rapid sideways movement to sever the fibres to the frontal lobe. In the 40s and 50s, an estimated 50,000 patients were given lobotomies worldwide.

But it quickly became apparent that the side effects were, to say the least, undesirable. "It was very crude," says Henry Marsh, a consultant neurosurgeon at Atkinson Morley's Hospital in London."But in the days before they had major tranquillisers, it had some kind of a calming, sedative effect. Of course, you could argue that having people doped up to their eyeballs in psychiatric units is a chemical lobotomy rather than a surgical one, but that's a moot point.

"The fact is that lobotomies were grossly abused. They weren't necessary and a lot of people suffered very severe personality damage."

With the appearance of effective drugs for depression and psychosis in the 50s, and with evidence of widespread abuse and appalling side-effects mounting, lobotomies were gradually discredited.

Or so it appeared. In fact, the operation has quietly survived the bad publicity. Today, in what its proponents call "neurosurgery for mental disorders", the holes cut in the skull are much smaller, and only carefully targeted sections of the nerve fibres are burnt out. With the aid of computers and imaging techniques, precise areas of the frontal lobe can be carefully "disconnected" in this way. There are various versions of the operation, involving different parts of the lobe and different methods of cauterising the brain tissue, but the procedure is still essentially a lobotomy. They just don't like to call it that.

Yesterday it was confirmed that 35-year-old Zavaroni, who weighed little more than three stone when she died, was being treated for chronic depression, not anorexia, at the University Hospital of Wales. In the UK this surgery is only used - as a last resort - in cases of severe depression or obsessive compulsive disorder.

It's likely Zavaroni fought hard to have the op. Unlike all other psychiatric treatments, lobotomies cannot be given without the consent of the patient in this country. Each year around 30 patients undergo such surgery, but before they are wheeled into theatre they are vetted by independent mental health commissioners, whose job it is to make sure that the patient is in his or her right mind and fully aware of the risks involved.

Keith Matthews is professor of psychiatry at the Ninewells Hospital in Dundee, one of the few centres in Britain to offer this psychosurgery. Surgeons at the unit perform the procedure on around six patients a year. "Our patients are usually people who have suffered from depression or obsessive compulsive disorder and have usually been exposed to just about every treatment available with nil impact," he says. The surgery is certainly far less destructive than it once was, but it remains highly controversial, largely because no one really understands how the brain works or why such procedures sometimes do seem to help.

Another big problem is that there have been no "gold standard" clinical trials. That would mean carrying out sham surgery on half the patients involved in the test - opening up their skulls, but not cauterising sections of their brains - to make sure that it wasn't the attention that was somehow making the patients better. Sham brain surgery was recently carried out in America on Parkinson's patients, but attracted fierce criticism as opening up the skull carries grave risks. It's unlikely it will be allowed here in the foreseeable future. "Trials need to be done," says Matthews. "But there are ethical problems."

Ninewells Hospital claims it's had impressive results. "What I usually tell patients before surgery is that it looks as though people are split into three categories after surgery," says Matthews. "A third do very well, with a major improvement, a third get some benefit and in another third it seems to have no significant effect."

Ian Reid, professor of psychiatry at the University of Dundee, insists that despite the stigma, the modern lobotomy can be a valuable tool. "It's difficult to appreciate how disabling severe mental illness can be," he says. "Some patients have spent years in hospital. But this surgery can bring about complete remission. It can have dramatic and remarkable effects."

These doctors are undoubtedly well-meaning - and confronted by someone as ill as Zavaroni was, such procedures may not seem that radical. But the simple truth is that this surgery destroys parts of an organ doctors are still struggling to understand. Mind, the mental health charity, wants the surgery banned. "It's irreversible and there's no evidence that it works," says a spokeswoman. "We can't find any justification for carrying on its use."