As well as the London Underground and subterranean mainline services, London is home to another set of train tunnels which run 70 feet under the streets of central London between Whitechapel and Paddington. The entire tunnel network is 23 miles long¹, was used up until May 2003, and was built for one purpose: to deliver the post.

The First Post Office Lines

The concept of delivering mail through tubes predates the original Post Office line by six years. In 1853, a small vacuum tube about 225 yards (200 metres) long was built to deliver letters inside a Post Office building. The system, now known as a Lamson Tube, became very popular, and in 1859 the Pneumatic Despatch Company was formed to build a larger subterranean line between the Post Office buildings. A test-line 450 yards (411 metres) long was built near Battersea, and the Post Office approved it. The first line was finished in 1863 between the North Western District Office and the parcels arrival area at Euston station nearby. The tunnel was built below the streets using the 'cut and cover' method², and trains ran on the vacuum system along a two-feet-wide track.

Despite problems with this first line, a second, much longer line was opened in 1865 between Euston station and the General Post Office building on St Martins Le Grand, calling at 245 Holborn on the way. The tracks on this line were three feet, eight-and-a-half inches (a little more than a metre) wide and also ran on the vacuum system. The line between Holborn and St Martin Le Grand was only properly functional from 1873, and a proposed extension to Pickford's on Gresham Street was never built. The line was not particularly popular with the Post Office as it only reduced the journey time by four minutes. In 1874 the line was abandoned and the Pneumatic Despatch Company was dissolved.

In 1895 another company known as the London Despatch Company formed with a view to reopening the tunnels and electrifying the lines. Although some work was done, the Post Office remained unenthusiastic about the line, and the work ceased in 1902, with the London Despatch Company winding up three years later. Surprisingly, the Post Office eventually bought the tunnel in 1921, but then it was only used for telephone cables. In 1928 there was an explosion in the tunnel under High Holborn, killing a worker and destroying half a mile of road. The explosion was blamed on coal gas, and during the road repairs some of the original pneumatic cars were found. These were damaged, but as luck would have it some more were found during work on Crowdale Road at Euston. These are now on display in the Bruce Castle Museum at Tottenham, and in the Museum of London.

The Post Office Underground Railway

Despite the chequered history of the pneumatic railway, the idea of a line underneath London to carry post was still considered a serious option by the Post Office, and so in 1909 a committee was set up to look into the various possibilities for such a line. They visited Chicago and Berlin to look at examples of successful lines, and concluded that a two-feet gauge electrically-powered line 70 feet (21 metres) below street level would be the most effective design³. The route of the new line was to include Liverpool Street and Paddington national rail stations as well as several Post Office depots including one in Whitechapel. At a total tunnel length of 23 miles covering a route less than seven miles long, and with suggestions to run 40 trains per hour, the project was ambitious to say the least. As usual, the Post Office were not particularly enthusiastic.

Work began nonetheless, with an experimental section being built 1915 by John Mowlem and Company, who had won the bid for the construction of the line. They completed the tunnels by 1917 using the Greathead shield system, but during the war the stations were put on hold due to lack of materials and work on the electrical systems was suspended for safety reasons. The tunnels found a use as a shelter for paintings from the Tate Gallery and the National Portrait Gallery, but work on the line eventually resumed in 1920, and the actual track-laying commenced four years later.

The first section between Paddington and the West Central District Office on Oxford Street was ready for its first trains in January 1927, with trains running to the Mount Pleasant sorting office by December that year. The entire line was ready for letter traffic by 1928, and after some initial problems the line was running regularly and as intended by 1932. So, just to make things interesting again, someone started a war.

1930s to 1980s

In anticipation of the Second World War, hinged bunk-beds were installed in the stations so that they could be used as night shelters for staff. This reduced the running hours to 16 hours during the day and evening. The shelters were used throughout the war, and the line suffered little bomb damage — the worst incident was the flooding of Mount Pleasant station after a direct hit in 1943.

Although several extensions to places such as London Bridge and King's Cross stations which were part of the original design were never built, the line still underwent some changes. The first of these was when the old Western Delivery Office closed in 1965, with another opening along with its own station on the railway. This meant the building of a 450-yard detour in the line, leaving a disused section which is now used for storage. This was the only major change in the structure of the line, and yet much more important things have happened to it recently.

The Rise and Fall of MailRail

The line was renamed MailRail in 1987⁴ when the entire stock was replaced with new trains in the classic Royal Mail livery. Ironically, this modernisation came around the same time as the advent of the Internet and email, and the line's days were already numbered. The line was already starting to lose money, and in 2002 Royal Mail announced that it was making a loss of £1.2million per day.

Recently, the King Edward Building and the West Central District Office were closed and sold, and so the stations at these buildings have been sealed off. The station at Liverpool Street mainline station also closed, and four active stations remained. After a review of spending in 2003, it was decided that MailRail should be mothballed, and that the sorting office at Paddington station should be relocated. The line finally closed in March 2003, having fallen victim to the Information Age.

The future of the line is doubtful unless it is resurrected using private funding. However, the line is being maintained in such a way that it could be reactivated overnight, whether to deliver post or for some more unusual reason. The line has been used once in the past to shoot part of the film Hudson Hawk, in which actor Bruce Willis is seen escaping through the Vatican's underground postal railway. It is possible that the line could be used for such things in the future, but with the competition from disused London Underground stations this is unlikely. The line once featured on the radio programme In Town Tonight when Brian Johnston took a ride on the line, pretending to be a parcel.

Just before closing, the line was carrying 30,000 mailbags per day, with each of the 50 trains taking 26 minutes to cover the seven miles, stopping for a minute at each station⁵. Each train would be loaded with 84 bags of letters and parcels, and would run at speeds of up to 40mph⁶ except for in the stations, where the reduced voltage applied to the rails decreased the top speed to 7mph.

The Structure of the Line

Although the line itself is 70 feet (21 metres) below the surface, the stations were built much closer to street level, meaning that the line must rise and fall along a one in 20 gradient near stations. There are two good reasons for this. Firstly, it is more convenient to have the stations nearer to the ground, as there is less distance for the letters to travel to the surface. Second, the shape of the line is also important in the way the line functions.

Instead of having every train controlled by a driver, the line is almost fully automatic. Trains are moved by switching on the current to the conductor rail of that section, and braked by switching the current off again. When a train is ready to leave the station, the engineer activates the first section of rail out of the station, but from thereon the train runs automatically. Imagine the line is divided into sections A, B, C and so on. When the train passes out of section A onto section B, A is deactivated by cutting off the current, but when it passes out of B into section C, A is reactivated for another train to use. In this way, no two adjacent sections of rail are live at the same time, and this greatly reduces the chances of an accident.

Extensions to the Line

When the line was first dreamt up, several extensions were to be made once the line was up and running. Two of these would run from near the Mount Pleasant sorting office towards the north, one of which would run in a loop serving Euston, King's Cross and St Pancras stations, while the other would run to the Northern Sorting Office. An even bigger planned extension was to run in a large loop passing as far south as Waterloo and London Bridge! Unsurprisingly these extensions were never built, although a few branch tunnels, each a few yards long, were built at the same time as the stations, with the most noticeable being those at Mount Pleasant.