In a unanimous decision, the Law Lords on Thursday overturned an earlier majority ruling by England's lower Court of Appeal that such evidence is admissable only if gathered in another country with no British involvement.
Home Secretary Charles Clarke dismissed suggestions that the ruling was a setback for the government's attempts to beef up legal measures to confront global terrorism.
He reasserted the government's opposition to torture, and stressed that the outcome would have "no bearing" on its terrorism policy.
In allowing an appeal against the controversial 2004 ruling by eight people detained under anti-terrorism laws, Lord Bingham of Cornhill, who led the panel of seven Law Lords, strongly condemned torture.
English law had regarded "torture and its fruits" with abhorrence for more than 500 years, he said Thursday.
"I am startled, even a little dismayed, at the suggestion (and the acceptance by the Court of Appeal majority) that this deeply rooted tradition and an international obligation solemnly and explicitly undertaken can be overridden by a statute and a procedural rule which make no mention of torture at all," Lord Bingham added.
The reference was to a rule of the Special Immigration Appeals Commission (SIAC), which allows normally inadmissable evidence to be accepted.
The detainees, arrested under legislation brought in after the 11 September 2001 attacks in the US, opposed a SIAC ruling that the Home Office, which authorises their detention, had "sound material" to back up the view that they were a threat to national security.
Human-rights groups have hailed
the Law Lords' ruling
The Law Lords' ruling means orders for their continued detention should be set aside and SIAC should reconsider the cases.
Liberty, one of 13 human rights groups which backed the appeal, described the ruling as an "incredibly important day, with the Law Lords sending a signal across the democratic world that there is to be no compromise on torture".
Its director Shami Chakrabarti added: "This is also an important message that distinguishes us from dictators and terrorists. We will not legitimise evidence obtained by torture by using it in our justice system."
London-based Amnesty International also backed the ruling but said it was "deplorable" that Prime Minister Tony Blair's government had to to be taken to court over it.
"Over the last two and a half years, the authorities have shamefully sought to defend the indefensible," it said.
Massoud Shadjareh, from the London-based Islamic Human Rights Commission, said: "It is the final nail in the coffin of the government's claim that torture can somehow be justified."
"So this issue is hypothetical. The real issue is the test applied. We do not expect this test to affect the outcome of these individual appeals"
UK Home Secretary
Clarke, the cabinet minister responsible for public security, said: "We have always made clear that we do not intend to rely on or present evidence in SIAC which we know or believe to have been obtained by torture."
"So this issue is hypothetical. The real issue is the test applied. We do not expect this test to affect the outcome of these individual appeals."
Clarke said it was one thing to condemn torture, but more difficult to find a "practicable solution" to terrorism that also serves the public interest and occupies "the moral high ground".