SHOAIB KHAN is 23 — but he has the surly demeanour of a teenager uncomfortable in his own skin. He is tall and lanky, and his flimsy physique has not curbed his hot head.

The fighting started when he was 14 or 15. He hit back at boys who taunted him for being a “loser”. At 20 he was running pitched battles with the neighbours, wielding a stick. He clashes with his mother, too — about the kind of young man he has become. A schoolteacher, she lets it be known that she doesn’t want a school dropout and petty criminal for a son.

During the summer months, Shoaib works in a shop repairing air-conditioners. He stopped passing end-of-year exams when he was 12. He wasn’t interested in school and, in any case, he could never concentrate. When he skipped lessons he just sat alone at home, while his mother was working. “I was afraid to be alone,” he says. “I felt depressed.”

Lurking beneath the tribulations of Shoaib’s short troubled life is an event no generation has experienced before or since: the world’s worst industrial disaster. It is 20 years since the American-owned Union Carbide pesticide plant leaked poisonous gas into the air around the Indian city of Bhopal, the capital of Madhya Pradesh, killing and maiming thousands of its poorest inhabitants.

The disaster seemed to have a predilection for children. Those under ten died in the greatest number and hundreds of pregnant women miscarried spontaneously. Like Shoaib, those who survived have been marked indelibly.

They saw people running from the cloud that burnt lungs and stung eyes like chillies. They stepped over shrouded bodies lining the streets and heard people calling to God to save them. Amid the crush of the stampede, many were separated from their parents. Thousands lost a mother or father, and many both. In the aftermath, they grew up in a sick city where greed and injustice was visible and officialdom inert.

“An entire generation in Bhopal has had a dysfunctional upbringing,” says Rajni Chatterji, head of psychiatry at Bhopal Memorial Hospital. “For those in their twenties, the impact is bigger than on the general population. I see huge personality problems, antisocial personalities and a lot of attention-seeking behaviour.”

Dr Chatterji finds cannabis and opium abuse and outbursts of aggression more prevalent than in previous generations. He adds: “Parents went through financial and social hardship because of the disaster and got busy trying to survive: widows had to fend for the family. We see young people who’ve had faulty or tough parenting. Many children were taken out of school and forced to work. Their whole lives have been about the tragedy, growing up amid the anger and frustration it has brought.”

Igniting the frustration is the fact that details of the event remain in dispute. The most commonly quoted figure is that 4,000 people were killed in the hours after the leak. But it is plausible that, given that 7,000 shrouds were sold in Bhopal in the three days afterwards, the number was double that. The number to have died subsequently from related illnesses is believed to be as high as 15,000, the death toll continues to grow and about 100,000 people are disabled by chronic symptoms. Union Carbide, now a subsidiary of Dow Chemical Company, has always claimed that the leak was a result of sabotage, but no one has been charged. Evidence, however, has pointed to poor safety and maintenance.

The victims do not believe that justice has been achieved. Warren Anderson, 83 and chief executive of Union Carbide at the time of the disaster, has yet to be extradited from either of his luxury retirement homes in the Hamptons or Florida to face charges of culpable homicide, as campaigners have demanded. The company’s lump-sum compensation payment of $470 million (£248 million) in an out-of-court-settlement with the Indian Government in 1989 was almost $3 billion less than had been demanded. Only half of it has been distributed to survivors.

Shoaib’s father, Ashraf, was an employee at the Union Carbide plant and its first victim. Three years before the gas explosion, he was splashed with liquid phosgene that spurted from a faulty valve. He died, in agony, 72 hours later. Shoaib was seven months and his older brother, Arshad, a toddler. Sajida, their mother, and the boys were thrown out of her in-laws’ house and forced to move to a down-at-heel neighbourhood.

On the night of the gas disaster, the family were travelling back to Bhopal by train from a visit to Sajida’s mother in the north of In- dia. They arrived amid the chaos, greeted at the station by the lethal vapour and a scene from a morgue. The platform was thick with a mass of people desperate to escape by train.

Like many in their twenties, Shoaib has sketchy memories of that night. He recalls that his mother, coughing and blinded by the gas, put him and his brother in the station waiting room so that she could look for a rickshaw to whisk them away. But Sajida collapsed outside and Shoaib, aged three, spent the night glued to that spot, clinging to his four year-old brother as he died.