A brief history of London’s post boxes and how you can tell their age, including when you can expect to see King Charles III’s cypher on them.
Royal Ciphers on Postboxes: a Brief Guide – HistorianRuby: An Historian's Miscellany
A look at London's post boxes from Queen Victoria to Queen Elizabeth II
City of London Police Boxes: Which is Your Favourite?
The scandalous history behind one post box in Liverpool city centre - Liverpool Echo
Spotting a Royal Cypher - The Postal Museum
Take a Letter: The Post Boxes of Gosport - Gosport Heritage Open Days
Penfold Hexagonal Post Box, North Street, NEW ROSS Td., New Ross
A look at London's post boxes from Queen Victoria to Queen Elizabeth II
Wall box - Wikipedia
Britain's Oldest Post Box, Blog
Sir James Murray's Post Box – Oxford, England - Atlas Obscura
Queen Victoria - Letter Box Study Group
A Post Box Odyssey — Ana Sampson
