In the US, the Postal Service has been scanning the address on envelopes for years and rewriting it along the bottom as a barcode which they print at the post o

In the US, the Postal Service has been scanning the address on envelopes for years and rewriting it along the bottom as a barcode which they print at the post office. They use their own code rather than the address you wrote to actually route the mail. It seems like this British version just moves the barcode to the stamp. When the address is optically scanned, the code number is associated with the address and can be used for physical routing going forward. That means the system is for their convenience, not the user's. It may reduce the amount of OCR scanning that's necessary, it removes the printing step, and it allows tracking and routing even before the OCR takes place.