But Cherie Booth, QC, also gave a ringing endorsement of the role of British judges in acting as a safeguard over the acceptability of new rules to combat terrorism.

She backed a judgment last December by the House of Lords that there should not be an absolute ban on the Government’s acting on intelligence possibly obtained by torture. But the law lords were right to say that such intelligence should not be used in courts, where someone’s guilt or innocence was at stake.

Her comments come as the Prime Minister is under increasing pressure to criticise the United States over its dealings with terror suspects. Tony Blair has angered campaigners by his refusal last month to criticise President Bush over Guantamano Bay or the use of so-called extraordinary rendition flights.

In a speech at Chatham House, the international affairs organisation based in Central London, Ms Booth avoided any overt reference to either issue. But she made clear her view that nothing could be invoked as a justification for torture: the international treaties that prohibit its use were absolute and should be adhered to, with “no exceptions whatsoever”, even in a state of emergency or war.

She added that international conventions allowed prosecutions against those who permitted torture from “the foot soldier, commanding officer, political official or head of state”.

Ms Booth added that in their landmark ruling before Christmas, the law lords had been pragmatic to say that governments may use evidence from abroad that may have been gained under torture if it could save innocent lives.

Equally, it was “altogether a different matter” where such evidence was brought before the courts, she said. Courts should not allow such evidence to be used “where the guilt or innocence of a person depends on that information”.

Ms Booth, speaking at the launch of Torture, a collection of articles published with the organisation Human Rights Watch for which she has written the chapter Sexual Violence, Torture and International Justice, emphasised that the UN convention against torture prohibited it in “absolute terms”.

“The convention could not be more explicit — no exceptional circumstances whatsoever, whether there is a state of war, or threat of war, a state of emergency or any other public emergency,” she said.

The QC called for a full and open debate on the challenges facing democracies in the time of international terrorism.

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