Magic has what Dr Walid, who would be the Folly’s resident man of science if he wasn’t actually resident in a nice Victorian villa in Finchley, would call a deleterious effect on microprocessors. We don’t know why doing a spell can reduce the chip set of your laptop to a fine sand, but since everything useful from your phone to your food mixer is controlled by chips these days it means you have to be careful. But just because you don’t know why something happens doesn’t mean you can’t attempt to quantify its effects.

And once you’ve quantified an effect, it becomes that much easier to weaponize it. All you need to do is modify your werelight a bit with a couple of formae inflectentes and, after about three weeks of trial and error, you have a projectable spell that will burn out every microprocessor within a conveniently small radius.

I’d got some stick from Nightingale, who has this strange idea that his apprentice should know what he’s doing before sticking his finger in the electric socket of the universe. But even he changed his mind when I pointed out that a) it was really just a beefed up werelight and b) you could use it to disable any car fitted with a microprocessor-controlled engine management system – which was pretty much all of them now.

Standing in the baking car park outside Morrisons I came this close to lobbing one into the white boys’ Micra, but even as I rehearsed the forma in my head I remembered the girls’ phones. According to the results summary from forensics, no data had been recoverable from either the phone memories or the SIM cards. But it hadn’t given a cause. There are plenty of things that can ruin your phone, but fewer things that are so thorough that a decent forensics team can’t extract anything useful. And one of those fewer things, I knew from bitter experience, was a burst of magic.

I gave the two boys a happy smile which almost caused the tall one to swallow his cigarette. Then I moved swiftly back to the Asbo, but not so swiftly as to give them the wrong idea.