It is banned, just indirectly
Have you tried to install an average (not top of the line) European lock in the UK to replace the POS that any beginner Eastern European crim can pick with a toenail? Show the cylinder from your "High Security" Yale/Masterlock/etc lock to someone on the other side of the channel. They will laugh their arse off hysterically.
I tried last week - I put a reasonably up-to-date German cylinder from a well known manufacturer. The model is sold widely on Amazon and used on the continent where it is considered minimal security (it barely gets past basic insurance reqs). It is combination of cuts and coded dimples - half way between a classic lock and a modern fully blown Euro Plus.
Well, the result was that I was peasantly surprised by finding that NOT A SINGLE key cutting service in the UK can cut keys for it. I will now have to cut keys for it in the local supermarket next time I am on the continent. So you choice for lock in the UK is either a POS which can be picked in under 15 seconds by a beginner Moscow/Sofia/Bucharest/Kiev burglar or a fully blown Euro Plus series coded lock which costs an arm and a leg and a prosthetic. It is quite interesting that you are also "encouraged" to disclose the latter on your insurance (and you know very well who has real time access to the insurance database).
Now, I wonder why this is the case... Historical examples come to mind. Stalin had all of the following banned for the general population:
1. Carrying and possession offensive weapons of any kind.
2. High security locks.
3. Encryption of any shape or form.
Hmm... Interesting similarities here...