Image: post box showing ciphers of Queen Victoria and King Edward VII. This is one of six Edward VII post boxes in the vicinity of Gray’s Inn Road, London WC1.
From the website of Historic England:
“The roadside post box was introduced in Britain following the 1840 postal reform which provided for universal affordable postage. New adhesive stamps made pre-payment of postage easy. However, letters usually had to be taken to the nearest letter receiving office which could be miles away. This, together with the growth in demand for postal services linked to industrialisation and urbanisation, led to the need for many more convenient places where stamped letters could be deposited.
The novelist Anthony Trollope, a General Post Office (GPO) official sent to Jersey to make recommendations, provided a solution. He adopted a system used on the Continent of placing locked cast-iron pillar boxes at the roadside and the provision of regular collection times. His scheme began in the Channel Islands in 1852 and was extended to the mainland in 1853. Since these Victorian beginnings, boxes have usually carried the insignia, or cipher, of the monarch reigning at the time of placement.
More than 60% of current British post boxes carry the EIIR mark of Queen Elizabeth II or a Scottish crown. 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. The Letter Box Study Group has identified 171 boxes surviving from the short 1936 reign of Edward VIII.
Aside from the monarchical insignia, there have been various mostly evolutionary changes in the design and manufacture of post boxes. Some of the first post boxes were hexagonal in shape, but a wide variety of designs quickly appeared. 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. This design had its posting aperture positioned beneath a cap for greater protection from rainwater.”
From the website of Colne Valley Postal History Museum (In the grounds of: The Laurels, 109 Head Street, Halstead, Essex CO9 2AZ):
“Edward VII reigned for only 9 years but the postal network was still expanding and some very interesting boxes exist. The earliest Edwardian boxes were modified from the last Victorian designs, but midway through the reign the elaborate scroll cipher of Edward VII began to appear on post boxes. As the network grew, more boxes appeared in country areas such as…attractive lamp-post mounted examples. The small wall box would have been found in towns and in the wall of smaller sub-postoffices. A version which opens at the back, was also made to allow the Postmaster to empty it from inside the shop.”