Are you saying that UK law says you can have a folding pocket knife, but not if it locks open?  To me, that sounds equivalent to letting you have cars, but not cars with seatbelts in them.  A lock is a safety feature.
I'd be interested in hearing the reasoning behind  law like that.  Not to say we don't have our share of wonder-laws here in the US.  I remember reading about one law, some state in the south IIRC, where it was illegal to have a goldfish in a bowl on a public bus if the goldfish was swimming upside down.  The poor little guys don't do that unless they're already 99% dead, so why punish their owners further!
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