A SIKH activist who has been detained in Britain without trial for six years was freed yesterday after a European court ruled that the British government was violating the European Convention on Human Rights by keeping him incarcerated.

One hour after the judgment by the European Court of Human Rights in Strasbourg, the Home Secretary, Mr Michael Howard, ordered the release of Mr Karamjit Singh Chahal, a prominent supporter of an independent Sikh homeland.

Mr Chahal was promptly ushered out of Bedford prison, in central England, having been there for exactly six years and three months, minus a day.

Mr Chahal, who took up residence in Britain illegally in 1971 had travelled to the Punjab region of India in 1984, shortly before the Indian army stormed the Golden Temple of Amritsar. Punjab police subsequently held and tortured him for 21 days.

On his return to Britain, he became a prominent figure in the affairs of British Sikhs. He was twice charged with assault and affray arising out of disturbances in temples, but on the first occasion the Court of Appeal quashed the conviction and on the second he was acquitted.

On August 14th, 1990, the Home Office decided to expel Mr Chahal for reasons of national security and the international struggle against terrorism.

Mr Chahal, who has been in prison since August 16th, 1990, has since been asking for political asylum, fearing that he would be arrested and tortured for his activities if he were to return to India.

In their ruling, the European Court judges unanimously found that Britain had violated two parts of the European rights charter that assert a detainee's right of recourse to the courts.

While there was no reason to doubt the British government's view that the Sikh activist was a national security threat, his deportation would have exposed him to torture and ill treatment in India, the judges said.

They did not, however, rule that holding Mr Chahal for so long was in itself a violation of the European Convention on Human Rights.

Mr Chahal is the father of two teenage children, both British citizens.

Yesterday's judgment in Strasbourg was the second setback of the day for Mr Howard, after the High Court in London faulted him on the way concurrent sentences are calculated.

Some 50 prisoners are to be immediately released as a result of the High Court ruling, while 800 others are to have their terms reduced.