Amid growing fears of copycat attacks and rising community tensions, Richard Barrett said preventing such terror attacks was “incredibly hard”.
As if to illustrate his point, two RAF fighter jets had to be scrambled yesterday to escort a Pakistan airliner to Stansted airport, Essex, after two passengers tried to get into the cockpit. The plane, which had been bound for Manchester, landed safely and two men were arrested.
In Warwickshire, police shut the M6 in both directions near Coventry while a “suspicious vehicle” was investigated.
And London Bridge railway station was closed as police were alerted to a man with an axe. Passengers were allowed back in and services resumed after about half an hour.
David Cameron was warned of the danger of follow-up attacks at a meeting of Cobra, the Government’s emergency committee, as military bases were put on high alert.
Killers Michael Adebolajo and Michael Adebowale were both known to MI5 but were classed as fringe figures who did not merit full scale monitoring.
MI5 chiefs are facing tough questions about how much was known about the two men and when they were last “on the radar”. But Mr Barrett, ex-head of counter-terrorism at MI6, believes there was little MI5 could have done to prevent the murder of Drummer Lee Rigby.
“I think it is incredibly hard to stop,” he said. “When does a person who expresses radical views, who joins a radical group, flip over to be a violent extremist? To find the signals, the red flags as it were, I think is enormously hard.
Read more: express.co.uk