Phil, this sounds like a right ball ache mate - I hope your friend manages to sort it out and get back to some normality ??
.......... I'd prefer gun laws like the Yanks.
If it were me, I'd get a couple of decent sub 12 springers now and take my mate for a shoot - it's relaxed and simple. He might even enjoy that..... no feckin about with bolts, bullets and rifles that need to be secured, no worrying about overshoot. Just a good day with a mate and a flask of tea ??