Ex-MI6 chief says it's 'incredibly hard' to stop terror attacks

A former head of Britain's foreign spying apparatus, MI6, has said that preventing terror attacks, including incidents like the Woolwich murder, was "incredibly hard".

Richard Barrett, former head of counter-terrorism at MI6, believes there was little MI5 could have done to prevent the murder of Drummer Lee Rigby.

Killers Michael Adebolajo and Michael Adebowale were both known to MI5 but were classed as fringe figures who did not merit full scale monitoring.

Express.co.uk quoted Barrett, as saying that it is incredibly hard to find the signals, as to when a person who expresses radical views, flips over to become a violent extremist.

Lord Blair, former Metropolitan Police Commissioner, said there were "thousands and thousands of people who listen to Islamic extremists". MI5 and MI6 must go after the most dangerous suspects who travel abroad for terrorist training, he added.

Lord Blair said the Security Service (MI5) has limited resources, and must prioritise people who are most likely to move from being interested in violent extremism to carrying it out. He said even if they have the resources to do it, they have to have a very high level of suspicion to put surveillance on them.

There are believed to be at least 3,000 people on MI5's database of extremist suspects.

Adebolajo, 28, and Adebowale, 22, both recent Muslim converts, are under arrest at separate London hospitals. Two women held on Thursday on suspicion of conspiracy were released yesterday. One man remains in custody.

A post mortem examination has failed to establish whether Drummer Rigby was killed by the car driven at him before he was attacked with knives and a meat cleaver.