The difficulty with these "money owing" letters is that you don't know what they are until you traipse all the way to the ruddy Delivery Office ! They could be a small package or perhaps something else of value, instead of yet another Xmas card. I have got them for the last 2 years, and they are a nuisance.
People should send the cheapest Xmas cards that they can buy, not these expensive thick ones, because its normally the thickness and weight that is the problem. People just stick a 2nd class stamp on without thinking.
The days when the Post Office was a public concern are long gone. They are now out to make as much money for the shareholders as possible, the net result of yet another unnecessary privatisation.