You can keep your privacy, but most people will not bother. Most people will buy stamps with a card (or phone) payment so there is a complete chain of identify.
The aim is mass surveillance so a few people going to the trouble of avoiding it is not a problem. True, it is meta data (not letter contents) but we know that is pretty powerful by itself.
I do mean it is the aim - they never really explained what the real advantages of doing it for, and I suspect there is pressure from the security services who are accustomed to seeing most communications (or at least most meta data) to seal what they see as a hole in data collection.
Using cash to buy them is not hard and the odds of anyone going through the CCTV is low unless you are going to post anthrax to the PM or something. I imagine the main reason to do it was to make it harder to use fake stamps, although there may be some tracking going on.
The aim is mass surveillance so a few people going to the trouble of avoiding it is not a problem. True, it is meta data (not letter contents) but we know that is pretty powerful by itself.
I do mean it is the aim - they never really explained what the real advantages of doing it for, and I suspect there is pressure from the security services who are accustomed to seeing most communications (or at least most meta data) to seal what they see as a hole in data collection.