Which may sound like a joke, but when trainspotters - who are about as dangerous a rained-on khaki bobble hat - start complaining about regular harassment, policing is seriously broken.

I didn't make this up. There was an ancient law in NYC prohibiting photography in subway stations. Nobody took any notice of it, until some newspaper published pictures of exposed wiring in a station, and the city filed changes. The main outcome was that the law was changed, but after 9/11 they quickly started trying to figure out how to bring it back.

I presume that any self-respecting terrorist will take pictures with his phone, rather than doing something more obvious like these photographers have been doing. They'll just have to prohibit using your phone near a train station,  I guess.