The Prime Minister has been criticised by his independent reviewer of terrorism legislation for comments he made about an anti-terrorist raid.

Politicians’ comments on anti-terrorist investigations were seen as “an unwelcome distraction” by the police involved, according to Lord Carlile of Berriew, QC.

In his report on the arrest of 12 terror suspects in raids in Liverpool and Greater Manchester in April, Lord Carlile criticised the comments made by Mr Brown after the raids. The Prime Minister had said the operation was aimed at preventing what he called a “very big terrorist plot”.

Lord Carlile said: “Certainly it is unusual for the Prime Minister to say anything about arrests that have just taken place, especially when the suspects have not been charged.”

Lord Carlile’s report on the arrests added: “Understandably, senior police officers regard statements by politicans about recent arrests and current operations to be an unwelcome distraction.”

He said that while it was impossible to to erect a wall of silence around events arousing great media interest, advisers to the Prime Minister and other members of the Government should take account the distraction their comments cause officers investigating alleged crimes.

The report criticises counter terrorism police for failing to take legal advice in advance of the arrest of the 12 suspects.

Greater Manchester Police failed to consult senior lawyers dealing with terrorism at the Crown Prosecution Service during the operation, the report said.

The experienced CPS lawyers were only contacted the day before the arrests in April this year and only met CPS lawyers six days after the men had been detained.

Twelve men – all but one of Pakistani nationality – were arrested on April 8 and all were later released without charge. Some of the men are applying for a judicial review of the decision to arrest them.

But Lord Carlile said there was enough evidence to justify arresting some of the men as part of the counter terror investigation known as Operation Pathway.

He highlighted an e-mail, published in the report, that caused officers serious concern. The e-mail referred to a “wedding” and stated: “They said you should be ready between these dates.” The dates were April 15 and 20, causing police to fear a terror attack was imminent.

The e-mail referred to an affair with a woman called “Nadia” and the sender said they were “getting ready for the big day”.

Lord Carlile said: “The intelligence assessment of the e-mail was founded on the experience of several years of intense scrutiny and policing of al-Qaeda in the UK and ... around the world. Throughout the period of police interest in the group, no women had been seen, and there had been absolutely no signs of wedding preparations. Simliar odd language had been used previously in relation to two major terrorism conspiracies which had resulted in trials and convictions.”

The e-mail and other intelligence, including photographs, led police to decide to make the arrests.

The report names Abid Naseer, a computer studies student at Liverpool John Moores University, as the man thought to have written the e-mail.

He was seen as the “central figure” behind the alleged plot, and the link between the Manchester and Liverpool suspects. He was linked to al-Qaeda and intelligence material suggested he was in direct contact with a foreign-based terror cell.

The report added that analysis of intelligence material strongly suggested to MI5 that he might be part of a “very significant” international terror plot.

Lord Carlile warns in the report that allowing intercept evidence in terror trials would “be wholly at odds with the national interest”.

He came down firmly against allowing evidence from phone taps to be allowed as evidence in trials.

He added that changing the law to permit the use of intercept evidence would place a “significant” new burden on those involved in fighting terrorism and tackling serious crime.

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