RE: RMG proposed changes. CHAPTER 111 Jul 2022 11:33
"green" is the reason being given but as only 6% of post is apparently moved by air, then it seems more likely Royal Mail just want to move the mail deliveries to later in the day, so that it can be delivered with the "next day" parcels as they usually arrive mid morning, rather than send them out on separate delivery runs.
Perhaps as mail drops and parcels increase in years to come that may make sense but I can't see it does at present. No other company would try and deliver letters to addresses in the dark, or, probably, 30C temperatures in mid afternoons.