Before speaking, Adrian Laing takes a small, precise sip of his cappuccino and carefully wipes away the specks of froth from his top lip. 'When people ask me what it was like to be RD Laing's son,' he says, 'I tell them it was a crock of shit.' He laughs, shaking his head.

The question of what it was like to be the child of one of the 20th century's most influential psychotherapists has been playing on Adrian's mind of late. 'It was ironic that my father became well-known as a family psychiatrist,' he says, 'when, in the meantime, he had nothing to do with his own family.'

As Adrian speaks in a modest north London cafe near his Highgate home, the same paradox is being pondered by a handful of mourners gathering a thousand miles south on the Balearic island of Formentera. It was here, on this windswept rocky outcrop, that the decomposed body of Adrian's half-brother, Adam, was found by police 12 days ago. Adam, RD Laing's oldest son from his second marriage, was discovered in a tent pitched on private land, the floor scattered with the detritus of a drunken night. Next to him lay a discarded vodka bottle and an almost-empty bottle of wine.

Initial police reports suggested that Adam, 41, had taken drugs and might have been on a suicidal binge following the end of his relationship with a long-term girlfriend, Janina, earlier this year. The post-mortem found that Adam, a tall, well-built and seemingly healthy man, died of a heart attack.

Conjecture about his death continued, rumours swirling around the beachside bars and restaurants of the island. There was talk of Adam's partying lifestyle, his free-spirited take on life and his occasional bouts of depression and heavy drinking. Over the last few years he had made a haphazard living skippering yachts for day-trippers or as an odd-job man in the quiet winter months. He was a regular at the Bar es Cap, where owner Mariano Mayans remembers him as 'a good man who liked his drink but could handle it.' A sailor at heart, Adam had crossed the Atlantic 11 times and was, by all accounts, a restless soul.

'He was a bit wild but a good guy,' says Nicholas Scherr, who moors a yacht on the island. 'He needed the challenge of the ocean.' Adrian adds: 'Adam found his own way in life. He was a lovely guy and it was a shock to hear of his death. I think it will take some time to sink in.'

Friends say he had grown melancholic since his separation from Janina, a German diving instructor, at the end of last year. He moved out of the house they shared in Cap de Barberia, a tranquil corner away from the tourist beaches. At first he looked after Scherr's yacht in the port of La Savina, sleeping on the boat. Then, a month ago, in an increasingly fragile state of mind, he erected a tent in a wooded area near Janina's home, on private land owned by a British couple he knew. It was here that his body was found, in an isolated field far away from home, accessible only by criss-crossing dusty tracks. It was a lonely way to end a life.

'I think he was depressed before he died,' says shipwright Jorge Agusti. 'He had split up with his girlfriend of four or five years and he had no work organised. He was not short of money but he was saying he was ready to leave. Adam was at the point of packing his bags.

'He liked to drink but he could take it. I saw him a few days before his body was found, and we went on drinking into the night. He seemed all right at the end.'

But Adam was not all right and, despite his outgoing demeanour, had not been for some time. 'I think Adam caught the depressive mood from his father,' says the psychotherapist Theodor Itten, a former student of RD Laing who later became a close family friend. Dr Itten says the break-up of his parents' marriage - Adam's mother, Jutta, separated from Laing in 1981 - affected him badly. 'When he was 13, 14, 15, he was rebellious, he dropped out of school. I think that was a very sad period of time for Adam. He tried to soothe it with smoking, sometimes with drugs and with drinking as a sort of self-medication.

'His death came as a shock. I sometimes wondered if he would get lost on one of his travels on the ocean or break his neck skiing down a wild mountainside. He was a very adventurous young man. Whatever the circumstances [of his death], perhaps he didn't have enough energy or power in him to deal with life.'

Many of Adam's friends on the island he made his home had no idea who his father was. 'He never talked about him,' says Hector Puig, 47, a handyman. If they had known, they might have been struck by the horrible irony that one of Ronald David Laing's lasting contributions to psychiatry in the 1960s and 70s was linking mental distress to a dysfunctional family upbringing. 'From the moment of birth [...],' Laing wrote in 1967, 'the baby is subjected to these forces of violence, called love, as its mother and father have been, and their parents and their parents before them. These forces are mainly concerned with destroying most of its potentialities. This enterprise is on the whole successful.'

Laing theorised that insanity could be understood as a reaction to the divided self. Instead of arising as a purely medical disease, schizophrenia was thus the result of wrestling with two identities: the identity defined for us by our families and our authentic identity, as we experience ourselves to be. When the two are fundamentally different, it triggers an internal fracturing of the self.

His theories overturned the prevailing orthodoxy of the day that mental illness was, as the German psychiatrist Karl Jaspers had put it, 'un-understandable'. He became a countercultural guru in the Sixties and Seventies, attracting a large anti-establishment following who admired his anarchic and individualist philosophies. Laing believed that mental illness was a sane response to an insane world and that a psychiatrist had a duty to communicate empathetically with patients. Once, when faced with a naked schizophrenic woman rocking silently to and fro in a padded cell, Laing took off his own clothes and sat next to her, rocking to the same rhythm until she spoke for the first time in months.

As a psychiatrist, both brilliant and unconventional, RD Laing pioneered the humane treatment of the mentally ill. But as a father, clinically depressed and alcoholic, he bequeathed his 10 children and his two wives a more chequered legacy.

This was partly a blighted genetic inheritance - Laing died, as did Adam, of a heart attack while playing tennis at the age of 61. He, too, struggled with drink and drugs, experimenting with LSD in his later years after being influenced by the work of the psychedelic drug pioneer Timothy Leary. But mostly, it was the result of an absorption in his work so total that he could be guilty of breath-taking callousness and seeming hypocrisy towards his own children. Adrian, 50, Laing's second eldest son, sees it like this: 'Anyone who has become deliberately well-known, inevitably they've done that at the expense of their family. They've gone their own way. They can't do both.'

According to his friends, colleagues and relatives, Laing was frequently unable to extend the compassion he felt for his patients to his own family. His children were left to grapple with their demons. Sometimes, as with Adam, it came with tragic consequences. For all his professional benevolence, Laing was a flawed parent. He, too, was capable of unleashing 'these forces of violence called love'.

Ronald Laing was five when his parents told him Santa Claus did not exist. He never forgave them, claiming in later years that the realisation they had been lying to him triggered his first existential crisis. For the rest of his life, his childhood memories were bleak. He told interviewers of an emotionally deprived upbringing in the Govanhill area of Glasgow, with a disciplinarian mother who broke his favourite toys when he became too attached to them.

His background left Laing with an abiding antipathy towards the nuclear family. By the time of his death he had fathered six sons and four daughters with four women over a period of 36 years. 'I think his reputation took some blows in terms of the way he died, leaving behind 10 children and looking like an irresponsible father,' says Adrian, the youngest of five children Laing had with his first wife, Anne. 'There was an enormous backlash then from families who thought he was blaming them for their children's mental illness.'

His own family was the first casualty of Laing's increasing celebrity. The reissuing in 1965 of his most famous work, The Divided Self, led to frequent television and radio appearances. In many ways his existentialist approach - he believed that social 'sanity' was fabricated by mutual consent; that the mentally ill were as fully human as the medics who were classifying them - captured the countercultural zeitgeist of the 1960s. His radical rejection of convention ensured he became the most famous cult psychiatrist in the country. Charismatic, darkly handsome and possessed of an innate sharpness of mind, he soon embarked on several extra-marital affairs, spending weeks and months away from the family home in northwest London. Anne was left behind, treading water in the wake of his success. The marriage finally came to a juddering halt in 1967, by which time, says Adrian, 'my mother had totally lost it. She found it so humiliating because he was becoming so well-known but he wasn't living with us.'

Laing had already started an affair with Jutta Werner, a German graphic designer who would become his second wife. Despite his burgeoning career, he paid only the legal minimum in child maintenance to his first family. 'He adopted an "out of sight, out of mind" mentality,' says Adrian, who started taking odd jobs aged 13 to contribute to the family income. 'In my mind, he confused liberalism with neglect. My mother was furious about it. She had an unfathomable amount of resentment. Her expression for him was "the square root of nothing".'

Laing would disappear for months on end, forgetting birthdays before turning up in a blizzard of misdirected anger. In a 1994 biography he wrote of his father, Adrian recounts one of Laing's rare visits to their new home in Glasgow when, having argued with Jutta, he took out his anger by beating his daughter, Karen.

He was an unpredictable, occasionally frenzied, father figure who acted with little regard for the consequences. When, in 1975, his second eldest child, Susan, was diagnosed with terminal monoblastic leukaemia, a row broke out between her parents. Anne felt it would be kinder not to tell Susan the diagnosis. Laing disagreed. In the face of fierce opposition from Anne, Susan's fiancé and her doctors, he insisted on travelling to the hospital to inform her that, in all likelihood, she would not live beyond her 21st birthday.

'That was the worst thing,' says Adrian. 'My mother just went potty. She said he was going to rot in hell for that. Then, after he told Susie, he went back to London and left us to deal with it. My mother was spitting blood.'

Susie died, aged 21, in March 1976. 'My father was riddled with guilt about it. He would have been aware of the statistics that demonstrate there is a higher chance of dying from that particular disease if you are from a broken family.'

A year later, Laing's eldest child, Fiona, had a nervous breakdown and was taken to Gartnavel Mental Hospital, Glasgow. Anxious that she should not be subjected to the brutal electric shock treatment and impersonal medical examinations that Laing so detested, Adrian called on his father for advice.

'I was really upset. I asked, "What the fuck are you going to do about it?"' Adrian pauses. A curious smile curls at the corner of his lips. 'At the time we were living in a house called Ruskin Place, and his response was: "Gartnavel or Ruskin Place, what's the fucking difference?" It was a double-bind, you see. Either he had nothing to do with it [Fiona's breakdown] and his theories were shit, or he had everything to do with it and he was shit.'

But how on earth could RD Laing, the celebrated psychiatrist whose entire reputation rested on his theories espousing the compassionate treatment of the mentally ill, reconcile his professional position with his personal behaviour? How could he empathise so profoundly with a naked, rocking schizophrenic patient he had never met and yet fail so spectacularly to do the same with his own daughter?

Adrian leans forward, resting his elbows on the stainless steel cafe table. 'In terms of how he rationalised it... erm... I'm not sure that... I don't think my father felt he was the cause [of the breakdown] so he wouldn't feel it was hypocritical.'

Later he tells a revealing story about Susan being interviewed in 1974 by a journalist writing a feature on the children of famous people. The piece ended with a memorable quote from her: 'He can solve everybody else's problems but not our own.'

The Hungarian psychiatrist Thomas Szasz puts it a different way. Laing, he wrote in 2004, displayed 'an avoidance of responsibility for his first family, indefensible since his line had been that the breakdown of children could be attributed to parents and families.'

But Laing seemed to mellow with the passing of the years. To his second family with Jutta - Natasha, now 38, Max, 32, and Adam - and to his two youngest children with different women - Benjamin, 23, and Charles, 20 - he proved a more kindly father. Adrian was gradually reconciled with him over the years, coming to stay with his half-siblings when he studied for his bar exams in London. 'Ronnie was clear, kind, warm-hearted and sagacious,' says Theodor Itten, who knew him in this later period. 'He was very gentle with his family. Once he told me that in his first family he had hit his children because he didn't know any better. I was surprised because I always thought Ronnie had been the Ronnie I knew, very playful and comforting as a father.'

Many of Laing's friends and colleagues speak of his extraordinary intuition and say he could read people with disarming precision. When sober, it was a talent that could reap rewards by winning someone's trust, whether a girlfriend or a patient. 'He had the gift of being open, of being honest,' says Sue Sünkel, 57, the German-born psychotherapist who gave birth to Laing's ninth child, Benjamin, in 1984. 'I'd never met anybody like him. He didn't feel the need to fix you. He wasn't afraid of people's pain; he was open to it and open to his own.'

But in his later years, as he became more dependent on alcohol and drugs, his judgment was blunted. When he was drunk Laing could exploit the fault-lines in someone's personality with a vicious cruelty. One of his students, Francis Huxley, once said that Laing's words could act like 'a psychic fist hitting the navel of insincerity'.

'My father was deeply intuitive and could make you feel you were talking rubbish just by looking at you,' says Adrian. 'It was very unnerving. He could pick up every nuance of your gestures and body language. When he was drunk he would rant and rave and it felt quite dangerous. He could be emotionally vicious. If he thought I was talking rubbish, his favourite expressions would be "psychotic" or "offensive", and I would say "Why don't you just say you disagree with me, Dad?" It was just so tiring. He was such a heavy drinker and I watched his second marriage disintegrate. Jutta would plead with him and say, "Where are you going to be in five years?"'

In 1987 Laing was forced to withdraw his name from the General Medical Council's medical register after a patient accused him of drunkenness and physical assault (the complaint was later withdrawn). He began to hold 'rebirthing' sessions and took spiritual pilgrimages to Sri Lanka and India. Much of his later work was erratic, crude in tone and increasingly discredited by mainstream psychiatry. 'The general view of Laing's theories within psychiatry is that they are the product of a wild, utopian, romantic imagination - or interesting as museum artefacts but of no contemporary relevance,' says Daniel Burston, author of The Wing of Madness: The Life and Work of RD Laing. 'The view outside psychiatry is more complex.'

What about the view of Laing's own family? Does Adrian believe the drunken disintegration of his father had a lasting effect on Laing's children? 'I think the entire family is a paradigm of cause and effect,' he says bluntly. 'With Adam... there's a sense in which... some people, if their father's an alcoholic, will turn into alcoholics themselves. After my father and Jutta sold the family home, that was when he really found himself on his own, at a relatively young age. He wore his heart on his sleeve. He never had children, he had girlfriends and there was never that much time between them. I would have liked to have seen him happy, settled with kids, but he just didn't like being tied down. He liked to feel free.' He trails off. 'It's a pity we didn't get the last episode of that story.'

Adrian says he has now made his peace with the infamous RD Laing, especially since becoming a parent himself (he has five children). In his biography of his father, Adrian drily notes that his relationship with him 'has improved greatly since his death'. 'I'm very relaxed about him now,' he says. 'I had enough occasions before he died to let him have it. We were friends.'

For all his inconsistencies, there is little doubt that Laing loved his children, in spite of the flawed manner in which he expressed it. In one of his later works, The Facts of Life, Laing wrote: 'Whether life is worth living depends for me on whether there is love in life.'

As Jutta and her two surviving children paid their last respects to Adam at a private cremation on Friday, perhaps they remembered the essence of these words. Perhaps they recalled the Janus-like brilliance of their late husband and father, his gentleness and his wildness; his charismatic charm and his unpredictability; the sharpness of his thoughts, and the drunkenness that blurred them.

Today they will scatter Adam's ashes over the ocean he knew so well. Despite his chaotic life, Adam Laing did have his family's love. Perhaps his father might have judged it a life 'worth living'.

Shrink wrapped: The life of RD Laing

Personal Life

· Born Ronald David Laing, 7 October 1927 in Glasgow.

· Studied medicine at Glasgow University.

· Fathered 10 children by four women.

· Died of a heart attack on 23 August 1989 while playing tennis in St Tropez, France.

Theories

·Laing helped popularise psychology detailing various forms of madness in The Divided Self (1960)

· Attributing schizophrenia to bad parenting is Laing's most criticised idea, put forward in Sanity, Madness and the Family (1964).

· In The Politics of Experience (1967) Laing argued that it is not people who are mad, but the world.

Controversies

· Took LSD with patients and drank heavily.

· Forced to withdraw from the medical register of the General Medical Council in 1987 after an accusation of drunkenness and assault.

Katie Toms