As it happens it's not typical British hysteria. There have been two very serious attempts to attack UK rail systems using IEDs within the last two years, one of which was found pre-initiation and the other of which only partially detonated, but that was down to incompetence rather than lack of will on the part of the perpetrator. If it had fully detonated there would have been multiple fatalities.
As I've said before See it, Say it, Sorted is an earworm; it's designed to get into your head so that if you do see something suspicious you'd be more likely to report it. If you want to ignore a still actively existing threat that's up to you.
It might be an ear worm - I can hear it immediately fully ingrained, from the "if you see somthing..." all well and good - job done right?
no - I couldn't tell you what the BTP text number is..