When you hear the term “domestic extremist”, whom do you picture?

How about someone like Dr Peter Harbour? He’s a retired physicist and university lecturer, who worked on the nuclear fusion reactor run by European governments at Culham in Oxfordshire. He’s 70 next year. He has never been tried or convicted of an offence, except the odd speeding ticket. He has never failed a security check. Not the sort of person you had in mind? Then you don’t work for the police.