Secret intelligence agencies, including MI5, will be able to veto the use of their phone taps as evidence in court, Gordon Brown has told MPs.

The Prime Minister has paved the way for intercepted material to be used in trials for the first time.

But in a statement to MPs, he said this would only happen provided it did not compromise national security.

A report from a committee chaired by Sir John Chilcot, a former Whitehall mandarin, accepted the principle of using wiretap evidence.

It said it should be possible to find a way to use some intercept material in trials, but many hurdles had to be overcome and a number of key conditions would have to be met.

These include giving the intercepting agencies "the ability to retain control over whether their material is used in prosecutions".

In addition, material gathered by tapping will not be disclosed to defence lawyers against the wishes of the agency originating the material - a condition that could prove insurmountable in view of court rules.

Defence teams will insist upon seeing the complete transcripts of any wire tapping - not just a few sentences thought important by prosecutors.

The Chilcot review also said that agencies should not be required to transcribe or make notes of material "beyond a standard of detail they deem necessary".

It has been a key concern of MI5 that their officers could end up having to transcribe weeks of eavesdropping.

Mr Brown said "further extensive work" was needed to see whether and how these and other conditions could be met.

He has ordered yet another review to consider whether intercept techniques and intelligence sources can be protected.

Campaigners have said using phone tap evidence would reduce the need to impose control orders on suspects.

But the review said there was no evidence that using intercept material would reduce the need for control orders.

Often the intelligence agencies can discern that a plot is unfolding by decoding the language used, but this would not be strong enough to stand up in court.

The review said that communications advances are already making tapping phones outdated in any case because most contact is by internet.

Britain is one of few countries to bar the use of evidence from intercepted phone-calls, emails, letters and faxes as part of a prosecution case.

David Cameron, the Conservative leader, called for a commitment for legislation as soon as possible, while Shami Chakrabarti, the director of Liberty, said: "If they can use phone taps in court all over the world without compromising security, why shouldn't we?"