Britain and the United States lost some of their moral authority through some of the measures they put in place after the September 11th attacks, Prime Minister David Cameron said.
Some measures, such as the establishment of the Guantanamo Bay detention camp, had been a mistake, Cameron told Al Jazeera television in an interview to mark the 10th anniversary of the Al Qaeda attacks on the United States.
"We can certainly see with hindsight and in some ways at the time, mistakes were made in that we lost some of our moral authority, which is vital to keep when you're trying to make your case in the world," Cameron said.
As he spoke, fresh allegations were emerging about the complicity of British intelligence agents in the illegal transfer of terror suspects following 9/11 to countries where they faced torture.
The Guardian on Saturday published claims by Libyan Islamist Sami al-Saadi, also known as Abu Munthir, that in 2004 he and his family were detained by MI6 and handed over to authorities in Libya, who allegedly tortured him.
They follow last week's claims by Abdelhakim Belhaj, now a rebel military commander in Libya, who said Britain and the US were complicit in a plan that led to his illegal transfer to Libya and subsequent torture.
Cameron set up an inquiry last year to probe allegations of British complicity in the torture of terror suspects after 9/11. It announced this week that it would examine Belhaj's claims.
Asked about the case, Cameron insisted: "Britain does not torture people. We do not believe in torture. We think torture is wrong."
But he said he set up the inquiry to "go through all the cases, including this Libyan case, to get to the truth".
According to the Guardian, Sami al-Saadi's case is the first in which British agents have been accused of orchestrating so-called extraordinary rendition, rather than simply helping US-led operations.
A spokesman for the Foreign Office declined to comment, telling the newspaper: "Our position is that it is the government's longstanding policy not to comment on intelligence matters."