Most operators it is even higher -- on average, pre-paid is probably 85 - 90% of customers. Many newer operators aren't even offering a post-paid option, as that would require a billing system, payment collection system, etc.

The UK is hardly the first country to introduce such controls. Switzerland notably introduced the requirement relatively recently, and threatened that lines that were not registered to a verified ID holder would be cut off.

Other countries more typically have a requirement, but it is laxly enforced. Hence, I have worked at a number of carriers in which "Mickey Mouse" was apparently our best customer, since he seemed to have thousands of SIMs registered in his name.