Locking blades are legal to own but not carry. Oddly, they seem to be more reviled by Authority than are fixed blades; a blade can be carried so long as one has "good reason" for doing so. However, good reason often depends on the judgement of ill-informed but well intentioned police officers. Locking folders are confiscated at the doors of official buildings if found. I lost a tiny Gerber LST this way when I took some students to the local magistrate's courts. My SAK was okay though.
The real illegal "weapons" are any kind of flick- or gravity knives, as well as push-daggers, knuckle duster knives and other such which are clearly designed for fighting. Unfortunately, the Authority often see locking blades as flick- and/or gravity knives. I fell foul of this when I tried to buy a Spyderco Manix II Moonglow and a Zero Tolerance folder from the US. According to customs they were gravity and flick-knives, both illegal and therefore destroyed. I can buy them quite legally from a couple of shops over here, but at much more cost.
I have a many more fixed blades than folders. Bizarrely, though, I have more locking folders than slip-joints or friction folders (both of which are legal EDC if under 3", so long as the police officer actually knows and understands the laws properly).
Rant over
