For nearly 80 years, it ferried post to sorting offices across London on more than six miles of track.
The capital’s Mail Rail, which linked sorting offices between Whitechapel in the East End with Paddington in West London, first opened in 1927.
Its closure came in 2003 when Royal Mail announced the line had become uneconomical with losses of £1.2million a day.
Plans to turn it into a system for delivering goods to Oxford Street shops or even wine never got off the ground. Nor did proposals to use the tunnels to grow mushrooms.
Today, part of the line is run by the Postal Museum as a tourist attraction, but otherwise it seems destined to be confined to history.
However, campaigners and former Mail Rail workers have suggested the service could be brought back amid increasing pressure on the postal service and congestion on the capital’s roads.
A spokesman for the Campaign for Better Transport said Mail Rail is a ‘ready-made solution’ to congestion in London and pointed out how van use in the capital has nearly doubled since the service ended.
Martin Longhurst, 60, who was an engineer on the ‘dinky’ line for more than 20 years, told MailOnline it would be ‘great to bring it back’, even if its use to transport post may no longer be feasible.
When it first opened, Mail Rail served eight stations across the capital. In its heyday it carried up to 12million letters every day to sorting offices across London.
From these depots, letters and parcels would be carried by rail and road to their destinations around the country.
At the time, the nation’s postal system relied on the rail network. Royal Mail’s Travelling Post Offices were specially adapted railway carriages that had been in use since 1830.
For a time, the trains boasted large nets which would snatch pouches of mail suspended from trackside equipment, whilst at the same time depositing post into other nets.
The heyday of the TPO network was in the 1930s, but after the Second World War concluded, the daily services were cancelled and the system never returned to its former glory.
The final TPO train ran on the night of January 9, 2004, and although a small proportion of mail is still carried on sealed train carriages most goes by road.
The idea for London’s Mail Rail – which was called the Post Office Underground Railway until 1987 – had its origins in a system that was devised in the 1850s.
Back then, officials suggested that mail could be transported in underground tubes, using air pressure as a propelling force.
Although experts said the scheme would work, the costs involved meant it did not progress further.
However, in 1863, a short pneumatic railway running nine feet underground between Euston Station and Eversholt Street less than half a mile away.
The wrought iron cars were sucked through the tube in around a minute.
Although trials continued until 1866, financial difficulties initially led to its demise.
The scheme was revived once again in 1873, when the line was extended to the General Post Office building near St Paul’s Cathedral.
Ultimately, the Post Office opted not to do a deal with the firm that ran the operation and so in October 1874 mail was carried for the final time on the track.
In the early 20th century, when mail was being severely delayed by congestion and fog, a committee was set up to look into developing an underground electric railway with driverless trains.
After the passing of an Act of Parliament, construction began in 1914 and tunnelling concluded in 1917.
However, Britain’s ongoing involvement in the First World War meant that the operating equipment could not be installed.
Instead, the new tunnels were used to protect art treasures owned by the National Portrait Gallery and the Tate Gallery.
The subsequent high price of materials after the conflicted concluded in 1918 meant that work on the railway did not resume until 1923.
The railway finally opened on December 5, 1927, with parcels initially running from Mount Pleasant in Farringdon to Paddington.
Deliveries to Liverpool Street opened later that year, whilst the service was extended to the rest of the line the following year.
The trains ran in a 9ft-wide tunnel on a 2ft gauge track. In 1930, new trains that could carry four mail bag containers had to be introduced due to excessive wear on the track.
Each container could hold 15 bags of letters or six bags of parcels. Another new fleet was introduced in 1980.
In 1993, a new centralised computer-controlled system allowed the entirety of Mail Rail to be directed from a single point instead of via separate control rooms at each station.
However, by the late 1990s – when an increasing proportion of mail was being delivered on the country’s roads – Mail Rail trains were only stopping at Paddington, Western Delivery Office, Mount Pleasant and the East District Office.
In 2003, the system was finally suspended by Royal Mail, despite opposition from workers and the London Assembly.
By then, sorting offices had been moved away from the rail line, making it less suited to the overground mail operation.
Backing calls for its return, Michael Solomon Williams from the Campaign for Better Transport, said: ‘Mail Rail is a ready-made sustainable solution to congestion on London’s streets.
‘Since Mail Rail was closed in 2003, van use on the UK’s roads has nearly doubled. While there are many fantastic solutions to ease congestion for postal delivery including cargo bikes and e-vans, Mail Rail provides a ready-made solution, and shows that rail has to lead the way in tackling congestion and pollution, and keeping us all connected.’
Mr Longhurst said: ‘It could be used for something that would get stuff across London a lot easier. It was there a long while and it did its job a long while.
‘If there was some sort of consortium that would get together to make use of it in an ideal world that be great.’
However, he also admitted that the system was ‘in a state’ when he left because there was ‘no real investment’ in its final years.
A Royal Mail spokesperson said: ‘We’re proud of our history and the input rail continues to have on our business to this day.’
A report produced in April 2003 by the London Assembly’s Public Services Committee talked up the environmental benefits of carrying post on Mail Rail.
They also highlighted suggestions for alternative uses for the system, including turning it into a delivery service for high value goods to shops on Oxford Street or even a wine transport network.
The report also questioned why Royal Mail had been running Mail Rail at less than a third of its capacity.
Officials concluded: ‘Members do not want to see the mothballing of Mail Rail become a long term or default position.
‘We recommend that Royal Mail move quickly to investigate ways of making the line cost-effective and with a view to putting it back into use (to carry either mail or other freight) for both its environmental benefit and for the benefit of Royal Mail’s shareholder who is, after all, the taxpayer.’
In 2012, a scheme was suggested to turn the former Mail Rail line into subterranean mushroom garden.
Fletcher Priest Architects, the firm behind the proposals, said the tunnels provided the ‘ideal environment for an urban mushroom farm with the introduction of daylight through a series of sculptural glass-fibre “mushrooms” at street level.’
They added: ‘These will highlight the route of the tunnel above ground and will convey daylight to the tunnels below through punctures along their length.
‘The produce will serve new pop-up concept “Funghi” restaurants and cafés at each entrance.’
Although the mushroom farm proposals never got off the ground, in 2017 the Postal Museum opened its tourist route on the track.
Two rains running along a section of the track entertain thousands of tourists every year.
This week, critics warned that a proposed shake-up of Royal Mail could mean the ‘death of first-class post’.
Households face seeing letter deliveries cut from six days a week to five – or even three – under proposals from the postal regulator in a bid to save the failing firm.
Another option would be for next-day delivery of mail to be scrapped altogether unless senders pay extra for an urgent service – meaning letters would take at least three working days to arrive.
The extraordinary cost-cutting proposals, after Royal Mail lost £1 billion last year, were set out by regulator Ofcom and faced an immediate backlash from small businesses, consumer groups, unions and Downing Street.
Asked about the plans, Rishi Sunak said he was ‘absolutely committed’ to the six-days-a-week service.
But it is feared that Monday-to-Saturday letter deliveries are unsustainable, meaning change is likely after the general election.
Royal Mail is in dire financial straits, having reported a £383 million loss in the first half of the current tax year. Ofcom’s proposals could save it up to £650 million.
Royal Mail says the current system is built for 20 billion letter deliveries a year, while it is now carrying out only seven billion.
The figure is set to fall to four billion within five years, while parcel numbers continue to climb.