The Brits have gotten very weird about weapons in general. Folding knives with lock-back blades are a no-no unless you can demonstrate a need. I prefer to carry a hatchet, way better than any lock-back or butterfly knife so that law wouldn't bother me but still I feel sorry for her majesty's subjects. Come to think of it, here in Philadelphia, I'd prefer to think my neighbor was packing heat rather than a hatchet under his jacket.
nial