Evil Terrorist Mastermind: You my friends have been selected to smite the crusaders. Here is an hundred grand - go and prepare bombs as you have been trained.
NHS Suicide Squad head off to the god-forsaken wastes of Blackburn or Glasgow or somewhere.
First NHS Terrorist: Right. We are going to use car bombs, so we need some cars. Let us consult the Exchange & Mart.
Second Terrorist: Sod that - I always wanted a Mercedes-Benz. Let's go to the dealership.
Third Terrorist: I concur.
(Terrorists buy nice shiny Mercedes (2 of), and a Jeep Cherokee, and show off driving them around for several months while accustoming themselves to the Land of the Infidel.)
First NHS Terrorist: I have received word: the attack is to be when the new leader of the infidels takes over. We must make our bombs. Where is the fertilizer?
Second NHS Terrrorist: ah... about the fertilizer
Third Terrorist: We had not enough money left after buying the cars. I blame the Jews.
First Terrorist: Oh shit. Well we must do the best we can. I'm going to B&Q to look for something that might blow up.
There's absolutely no reason to believe that's what happened, but whatever the real story is, it probably isn't any less stupid.
Oh, and do bear in mind that the whole NHS thing might be a bit of a red herring: the police seem to be rounding up telephone contacts of the self-immolationists, which in itself is a perfectly sensible approach, but I wouldn't be at all surprised if most of those arrested the last couple of days were to turn out to be innocent within the next few days.