Strangely, any recordings from phone taps on the public system are not admissible in British courts.
The intelligence community is Mr Clarke's biggest backer on this. It fears that allowing phone tap evidence to be heard in court could reveal its secret operational methods.
As it stands, tapes from conventional bugs - not attached to phones - can be used in court. Telephone conversations on an internal network can also be used and so can material where one of the people on the line is an undercover officer.
But a taped phone conversation between a suspect and a third party, on a landline or a mobile phone, is inadmissible. It can only be used for intelligence purposes.
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Liberty - the civil liberties campaign group - does not object to intercept evidence being used in open court with a properly constituted jury. However, Privacy International has its doubts, fearing phone evidence would be presented to a jury as fact.
http://news.bbc.co.uk/1/hi/magazine/4211745.stmSo it's possible they think they've got something from a phone tap, but know they won't be able to use that in court. So they apply for more time, hoping they'll get a confession, or something else will turn up. Now that they've got some charges, I doubt they're holding people without any suspicion of them at all - they've avoided looking complete idiots by having to release everyone without any charges (and they have already released one without charges).