Britain launched an attempt at the European court of human rights yesterday to overturn an 11-year-old judgment by the court which bans the deportation of suspected terrorists to countries where they face a risk of torture or degrading treatment.

The government has been trying for two years to find a way of challenging the Strasbourg court's judgment in the 1996 Chahal case, which has frustrated its attempts to expel suspects to such countries as Tunisia and Algeria.

It was given permission to intervene in a case brought against the Netherlands by Mohammed Ramzy, a 22-year-old Algerian terror suspect, but that case has been held up by procedural delays.

However, yesterday the court's grand chamber of 17 judges heard Britain's arguments when it intervened in another case, brought against the Italian government by Nassim Saadi, 23, a suspected terrorist and brother of a suicide bomber. He was convicted of criminal conspiracy in Italy and given a 20-year sentence by a Tunisian military court in his absence for belonging to a terrorist organisation abroad and incitement to terrorism.

Italy obtained diplomatic assurances from Tunisia that he would not be tortured and could reopen the criminal case against him, but his lawyer, Sandro Clementi, told the court yesterday that it had strong evidence that torture was "a daily practice" in Tunisia.

Britain hopes to persuade the court to reconsider its judgment in the case of Karamjit Singh Chahal, a Sikh militant who successfully argued that he should not be sent back to India because he would face a real risk of inhumane treatment.