The Post Office Underground Railway

During the early years of the 20th century operations at the Mount continued to expand – stimulated by a national annual volume of post that had reached a staggering 5.9 billion items by the eve of World War 1.

A significant percentage of this figure - and nearly all inbound international mail - passed through London. The problem of shipping a formidable number of mailbags between the capital's sorting offices and its major train stations needed attention.

To avoid London's congested streets, the Post Office decided to travel underneath them. Construction of the Post Office Underground Railway (later known as Mail Rail) began in 1914. Work was delayed by the outbreak of the First World War, but the unfinished tunnels were used to protect national art treasures from the Zeppelin air raids.

The completed railway had 23 miles of two-foot gauge track running through tunnels 70 feet below the ground. The line ran from Paddington Station in the west, to Whitechapel delivery office in the east. The electric trains carried no drivers – only mail – and were controlled by levers in switch cabins at each station. When it opened in December 1927 it was hailed by the press variously as 'The Robot Railway', 'Post Office Wonder Railway', and even 'The Ghost Trains run by Robot hands'.

Mount Pleasant station was the largest of the eight original stations. It was also home to the main train workshop where any maintenance was carried out. Original architectural plans from The Royal Mail Archive show the intricate planning required to integrate the underground railway with the existing sorting system at Mount Pleasant. As well as this, the engineers building the station and depot had to allow for the new, larger and heavier sorting machinery which was anticipated for Mount Pleasant in the coming decades.

The use of Mail Rail is currently operationally closed as it is no longer operationally viable. Neverless, it was a remarkable engineering achievement, of which the postal service can be justifiably proud.