Mr Clarke was hoping to win support for new anti-terrorist legislation that would let suspects be held for up to three months without charge. But the Scotland Yard document, distributed yesterday, contained details of three terrorist cases which are sub judice.
One of the cases highlighted by Scotland Yard has been described by a senior legal source as the biggest terror prosecution ever mounted in the UK.
The details of the cases cannot be repeated because doing so could amount to contempt of court, but they include evidence against a number of defendants and their behaviour in police interviews.
The media lawyer Rod Dadak said: "I would be most surprised if, in issuing a release seeking to justify new detention powers, any reference would be made to a case which has yet to come to trial. It is inappropriate to do so and clearly calls into question the risk of prejudicing a fair trial. The detail they have given impacts on the conduct of the defendants, which would appear to breach the rules with regard to contempt."
A Crown Prosecution Service spokeswoman said: "It is the CPS's view that the material that the document contains is not prejudicial to any future proceedings." She added that the document did not contain details such as individuals' names or dates or locations of alleged offences.
Scotland Yard said: "The MPS [Metropolitan Police Service] compiled a paper sent to the Home Office regarding proposals for three month pre-charge detention in terrorist investigations. A redacted version of this original document was considered by the CPS, who advised that publication in its redacted format would not constitute contempt of court."
A Home Office spokeswoman said: "There is no question whatsoever of the Home Office issuing material which might prejudice legal proceedings."
The Home Office distributed the Met's document to MPs, peers and journalists. Headings of each case study stated: "This case is sub judice and it would therefore be inappropriate to release further details" but went on to include information banned from publication ahead of a trial by the 1981 Contempt of Court Act.Reuse content