It is either a knee-jerk reaction or else it is a carefully considered statement, which is part of the process of conditioning us to accept further intrusion into our private lives. If the next atrocity is planned via mobile phone, will he call for the phone companies to monitor all calls? What about twitter?
I may well see things differently because I am aware that as an active & vocal supporter of the YES campaign, I, and thousands of my fellow supporters are classified as 'enemies of the British State' and thereby closely monitored. If MI5 et al would direct their efforts at real terrorists they might be more successful at keeping track of them.