Royal Mail have introduced bar codes on their stamps. Each stamp is now uniquely identifiable. The barcodes don't contain any personal information, but it will presumably be possible to determine the location and time of purchase, assuming the retailer scans the barcode on the book of stamps when you buy it. Aibu to think this will make people think twice about sending poison pen letters, especially the ones that might be nasty enough to warrant police investigation?
I haven't seen this mentioned anywhere - Royal Mail just say they are to improve security, with no detail on what they mean by that.