Every day I ask myself, 'Why am I here?'

Amid the drab surroundings of the visitors' meeting room at Bedford prison, inmate HD2167 presents an exotic spectacle. He stands to greet visitors, a massively bearded and turbaned figure wearing traditional kurtha pyjamas - long flapping white shirt and baggy trousers. As he bows and shakes hands in polite salutation, it is hard not to feel that he looks seriously out of place.

Karamjit Singh Chahal has been looking out of place for some time now. Five years and one month to be precise. "Every day I ask myself, 'Why am I here?' " he says as he sits down at the bare table.

Chahal appears to have good reason to feel confused. He has been incarcerated in Bedford since his arrest in August 1990, pending deportation to India for reasons of national security. Yet during that time, he has not been charged with any offence, or told what crimes he is supposed to have committed, merely that there are serious allegations against him concerning unspecified terrorist offences. His right to remain in Britain, where he has been a resident for more than 20 years, has been taken away with a stroke of the Home Secretary's pen.

"If there are allegations against me," he says, "all I ask is to be brought before a court so that I can answer them. If I have done anything wrong, I will happily leave the country." The Government, however, argues that Chahal is such a threat to public security that trying him in Britain would endanger "intelligence sources [which] require protection". It wants to expel Chahal to India, a country where, says Amnesty International, his "physical safety would be seriously jeopardised".

Chahal is a devout Sikh who supports the cause of Khalistan - a separate homeland for Sikhs in the Punjab. In the past decade, more than 20,000 have died in a civil war between Khalistani guerrillas and Indian security forces, during which time, says Amnesty, "thousands of known and suspected supporters of separatist demands have been detained under special legislation suspending legal safeguards. Scores of them have been tortured to death in police custody or have simply 'disappeared'." Chahal claims to have been detained and tortured during a visit to India in 1984 - an allegation denied by the Indian authorities, but one that the British Government does not dispute.

In July 1993, Chahal took his case to the European Commission on Human Rights. It issued a report this month condemning the British Government's treatment of him. His case will be heard by the European Court, probably next year. This inspires in Chahal relief but also regret. "I do not understand why this could not be settled here," he says.

Chahal was born in 1948 into a farming family near Amritsar, where he grew up chafing at the slowness of life in a provincial town and longing for adventure. "I had a sister who was living in London at the time," he recalls. "I was a young man who wanted to see the world, so I thought, 'Why not go?' " He arrived in Britain in 1971 on a visitor's visa and enjoyed himself so much that he decided to stay on illegally, taking various manual jobs.

In 1974, the new Labour government brought in an amnesty for illegal immigrants. Chahal owned up and was granted "indefinite leave to remain" (ILR) in the UK, a status of residency which, he now perceives, is at the root of his problems. For ILR does not offer the recipient citizenship, it simply offers a foreign citizen the right to live and work here. It can be cancelled at any time by the Home Secretary, who can have the holder summarily deported.

Having legalised his residency, Chahal settled down to a regular existence, working at the Ford car plant in Dagenham. In 1975, he visited India to get married, and returned with his bride, Darshan Kaur Chahal, who was also granted ILR. They had two children - a daughter, Kiranpreet, now 18, and a son, Bikaramjit, 17 - who are British citizens because they were born here.

Thus the Chahal story would have continued to this present day, had it not been for the recession of the early Eighties. Chahal was made redundant at the end of 1983 and, having received a large pay-off from Ford, decided to return to live in India. "I wanted my children to grow up among their family," he says. A preliminary visit was planned at the end of 1983 because Chahal wanted to attend his brother-in-law's wedding, despite evidence that political trouble was brewing in the Punjab.

He arrived in Amritsar in 1984, at a time of considerable turmoil. A Sikh religious revival was sweeping the Punjab, inspired by the fiery rhetoric of a charismatic preacher, Sant Jarnail Singh Bhindranwale, who was to die that summer when the Indian army stormed the holiest shrine of Sikhdom, the Golden Temple in Amritsar.

Bhindranwale's message was that Sikhs should rediscover their religion and struggle to free the Punjab from domination by Delhi. The hitherto secular Chahal attended several public meetings addressed by Bhindranwale and, by his own account, underwent a spiritual reawakening.

By this time, the Indian government had become alarmed by events in the Punjab and decided to crack down on Bhindranwale and his supporters. Among those arrested in a police round-up of Sikhs in Amritsar in March 1984 was Chahal, who was taken in for "questioning" - an experience which, he says, left him permanently deaf in one ear and with scars all over his body.

He was eventually released and returned to Britain, where he set himself up as a preacher to Britain's Sikh community. "I wanted to spread Bhindranwale's message that Sikhs should return to the pure forms of their religion," Chahal says. The message he preached in Sikh temples around Britain undoubtedly had a political, as well as a religious, content. "I supported the idea of Khalistan - of independence for Sikhs," Chahal says. He admits this freely, and that he became a member of the International Sikh Youth Federation, which campaigns for Khalistan among British Sikhs. However, he denies what the Government alleges: that he became involved in masterminding and financing terrorism in India.

In October 1985, Chahal was detained under the Prevention of Terrorism Act (PTA) on suspicion of attempting to assassinate the Indian prime minister, Rajiv Gandhi, who was visiting Britain. He was released and no charges were brought. The next year, he was arrested and charged with public order offences at a Sikh temple in Kent, after a fight broke out. The case was dismissed when Chahal established that he was not at the temple when the fight took place. A similar charge was brought against him in 1987, relating to a disturbance at a temple in east London: he was convicted of assault and causing an affray and served nine months in prison. However, the Court of Appeal quashed the conviction when it discovered that the evidence on which it had been based was untrue.

In 1989, Chahal's application for citizenship was rejected, despite 15 years residence, another indication that he was regarded as undesirable. But none of these "signals" prepared Chahal for being taken to prison the following August.

Stripped of his flimsy right to remain in Britain and knowing that he was to be deported to India, Chahal applied for asylum on the grounds that he would be exposed to the risk of torture if sent there. His application was dismissed by the Home Secretary, who claimed publicly that Chahal had "a violent involvement in Sikh terrorism".

Normally, an applicant so refused would be entitled to appeal to an independent tribunal. But because Chahal's case involved unspecified national security considerations, this procedure was denied him. Subsequent appeals for asylum have been similarly dismissed, as have any applications for bail, though in appealing Chahal has managed to delay his deportation.

Having exhausted all possible remedies in the UK, Chahal took his case to the European Commission of Human Rights. Free from the constraints of the UK judicial system, the Commission started asking the Government's lawyers some searching questions about what the security issues actually were. This elicited a list of what the Commission described as "untested allegations about [Chahal's] terrorist activities".

Anne Widdecombe, the Home Office minister, says: "Mr Chahal has been told clearly that his deportation has been ordered because of his involvement in terrorism, both in the UK and abroad." But why, if he has committed terrorist acts in the UK threatening British citizens, is he not being tried for such offences in a UK court? And why, if there is evidence connecting him with terrorist attacks in India, has the Indian government not tried to extradite Chahal?

The Home Office shows no sign of wanting to answer such questions. Meanwhile, Chahal wastes his life in jail. As he prepares to go back to his cell, I explain to him what the Home Office has told me: that he is free to leave the country at any time so long as he can find a third country which will accept him. This, he recognises, is going to be difficult for a man who has been publicly branded a terrorist. Chahal gives a resigned smile. Yet in that smile there is also fear, for he then says: "All I know is that if I am sent back to India they will kill me."