Britain said on Thursday it did not have enough evidence to prosecute men it is holding without trial under emergency anti-terrorism laws rushed through after the September 11, 2001 attacks on the United States.
But Attorney-General Lord Goldsmith said he still had no intention of letting them go. "If there were criminal offences which could have been proved by evidence, they (charges) would have been brought," he told the country's highest court which is sitting in judgement on the controversial detention laws.
"There is a difference between assessing whether somebody is a danger and whether someone has committed a possible offence. There are people who represent a real danger who have not committed a possible offence," Goldsmith added.
Nine law lords are hearing a final appeal over whether Britain had the right to impose special emergency measures, now used to hold 12 foreigners indefinitely without charge.
The test case is due to end on Thursday, with judgement reserved to a later, as yet unspecified, date.
To enact the law, Britain declared an emergency and suspended parts of the European Convention on Human Rights. Lower courts upheld the powers, but until now the law lords have yet to address the measures, as the US Supreme Court did earlier this year over the detentions of "enemy combatants".
Goldsmith said the decision to enact the draconian law was forced by the carnage of September 11.
The government concluded that Britain was a target, foreigners were part of the plot, and emergency measures were needed to cope with the threat, he added.
"You have got to decide as a Government, as a parliament, are you prepared to take the risk of taking no action against someone, who on reasonable grounds you believe to be a danger?
"It is a difficult balancing act, but it is a judgement which has to be made. Avoiding a threat is a risk assessment. The task of the Secretary of State is to evaluate risks in the context of national security," he added. Lawyers for the detainees, backed by human rights groups, argue the measures violate basic rights by allowing the state to lock up people based on secret evidence.