Yeah, butterfly knifes have been illegal since 1959 in the UK, I think. I also think that the multitool element is sufficiently blade-like to be considered a knife as opposed to a knife-like novelty item. It is a pity because I think that butterfly knives are a particularly safe knife to carry, but I guess that teddy boys must've been using them to menace upstanding citizens in the '50s or something. Well, I suppose that they are a weapon rather than a utility knife.
(I learned this by being prosecuted for carrying one, so this is wisdom that was gained at great personal cost.)