The suggestion is that "lone lunatics" don't wake up one day and decide to commit murder without there being any warning signs in advance. Even people who aren'

The suggestion is that "lone lunatics" don't wake up one day and decide to commit murder without there being any warning signs in advance. Even people who aren't in a cell are likely to exhibit changes in character, association and behaviour that could bring them to the attention of the authorities. One of the other things about the UK over the past 15 or so years has been the massive investment in "community policing". It has been a huge cultural change, police forces became police services. Thousands of PCSOs were hired and conscious efforts made to get officers out of cars and into communities building up relationships. While sources aren't revealed I'd be amazed if some of those 40 foiled plots hadn't been in part stopped due to better initial local intelligence rather than hi-tech GCHQ gizmos.