Greater Manchester Police, which manages the North-West Counter Terror Unit, last night rebuffed the criticism.

GMP’s Assistant Chief Constable, Dave Thompson, said officers liaised with the CPS before the arrests and there was a “compelling case” to act.

He added: “None of the conversations [with the CPS] would have changed our decision to make arrests or the number of people arrested.”

While the email spiked interest in the “cell”, the immediate trigger for the swoop was a major security breach by the Metropolitan Police’s Assistant Commissioner Bob Quick, who was photographed with top secret briefing papers on his way into 10 Downing Street.

The blunder forced the operation to be brought forward and the suspects rounded up in broad daylight.

Shortly after 5pm on April 8, dozens of police descended on JMU’s library brandishing guns. Terrified students were told to stay inside and keep away from windows.

Lord Carlile’s report says the police were right to go in heavy handed and “take no chances”. He said: “Whilst the arrests lacked visual subtlety, it is probably right that in such circumstances no chances should have been taken by the police.”