From Historic England:
“Boxes from the reign of George V account for about 15% of the total. There are smaller numbers, in descending order, of boxes from the reigns of George VI, Victoria, and Edward VII.”
“From 1857 wall box-type post boxes came into use for fixing into existing walls. In 1859 an improved cylindrical design of pillar box was created for standard use nationwide.”
“A Victorian wall post box on Cheyne Walk in Chelsea, London, UK. This is a large Allen wall box and is number SW3 43.
Manufacturer Inscription: WT Allen & Co, London (1881-1901)”