Ah, yes madcrate, I think you misunderstood. In the UK, before the rifles are sold on by a dealer, they have to be proofed by the commercial proof house. But only if they're sold in the UK. If they are exported, then they don't have to be UK proofed. In the UK, the 'authorities' don't/won't accept the tough and stringent military proof. Don't ask me why, I don't think anyone knows.
The UF serial number prefix was a specific UK Military requirement and many people seem to think that the wrapped No4's are all Irish contract.