Fresh calls for phone-tap evidence to be used in court cases involving terror suspects have followed comments made by England's top police officer.
Sir Ian supports plans to put terror suspects under house arrest
Home Secretary Charles Clarke has ruled it out, denying it would make it easier for terror suspects to be tried instead of being detained without charge.
But Metropolitan Police Commissioner Sir Ian Blair told the Daily Telegraph it would make policing "much easier".
Some argue such evidence would reveal methods used by intelligence agents.
Backing Sir Ian's stance, Shami Chakrabarti, director of human rights group Liberty, said: "Judges rather than politicians should decide when to authorise phone tapping.
"However, if it is legitimate to eavesdrop on someone's private phone calls, it is nonsensical not to use relevant material in a criminal trial."
But opponents argue that phone tapping evidence is often weak as it relies heavily on a mole to explain what people in the conversation are talking about.
This, in turn, could also jeopardise the mole if he or she is still working under cover.
Sir Ian told the Daily Telegraph: "I have long been in favour of intercept evidence being used in court.
"In policing terms it would make my job much easier."
The commissioner, who took over from Sir John Stevens on Tuesday, said the move would help relations with the Muslim community.
And he said it would allow the courts to weigh up the evidence.
"At the moment, nobody can test it," he said.
Tory MP Damian Green said the home secretary was stuck in a "peculiar old-fashioned mindset that the rest of the world had moved on from".
"Every other country in the world, barring Britain and Ireland, appears to allow this, and they are perfectly free systems, so I think we should as well," he told BBC News 24.
He added the Conservatives would move an amendment to the Serious and Organised Crime Bill on Monday to try to allow phone-tap evidence. And Mark Leech, founder of the national ex-offenders charity Unlock, said "it makes no sense" to withhold such evidence from a jury.
Under the Anti-Terrorism Crime and Security Act 2001 terror suspects can be held indefinitely without facing trial.
But the home secretary has announced a change in the law after Law Lords ruled the detentions illegal.
Mr Clarke will replace indefinite detentions with "control orders" where suspects will be but put under house arrest and surveillance.
On the threat of terrorism, Sir Ian said: "It is inevitable that terrorists connected to al-Qaeda will attempt to carry out a terrorist atrocity in London.
"I know that because they have. It is difficult to calculate whether it is inevitable that they will get through."
Sir Ian intends to ask for a further 5,000 officers to patrol London's streets.