Just how effective are our security services?

The disclosure by George Osborne last month that £100m had been handed to MI5 and MI6 in the past few weeks came as a surprise. But there was little criticism from civil liberties groups about such a large sum being given to spy on British citizens: the Chancellor timed his announcement a few days after the Charlie Hebdo murders.

The threat of British Muslims returning from Syria and Iraq to carry out attacks in this country is the all-consuming security concern at present; and this has been the reason given for the extensive monitoring being carried out now on telephone conversations and emails and the social media, as well as getting information from within the Muslim community.

The security and intelligence agencies want more powers on surveillance. The director-general of MI5, Andrew Parker, pointed out, again in the aftermath of the Paris attacks, that 50 per cent of his service’s work was now counter-terrorism rather than counter-espionage and all these investigations have the key requirement of intercepting communications.

Just how effective this has been in preventing the trek to the battleground is open to question. Dozens of young people, women as well as men, have been stopped from boarding flights with the aim of reaching Isis or al-Qaeda.

But many have also slipped through. One reason for this, according to security officials, is that a large number of those making the journey are not obvious terrorist suspects. It is very difficult to gauge when talk often based on bravado about joining jihad can turn into real attempts to do so. Even their families are often the last find out.

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