Seventy feet beneath London’s streets, a train about the size of a garden bench once ran at 40 miles an hour with nobody aboard and nothing inside it but other people’s letters.

That was the Post Office Railway, rebranded Mail Rail in 1987, a two-foot-gauge electric line running 6.5 miles from Paddington in the west to Whitechapel in the east. It had eight stations, each tucked beneath a sorting office, none of them open to the public. Records held by The Postal Museum date the opening to 5 December 1927, when the first parcels ran between Mount Pleasant and Paddington in time for the Christmas crush. At its peak the line shifted as many as four million letters a day.

No passenger ever bought a ticket.

An idea that took seventy years to arrive

Underground mail was not a 1920s brainwave. In 1855 Rowland Hill, then Secretary to the Post Office, sent the Postmaster General a proposal for firing letters through tunnels on air pressure, linking headquarters to a building at Holborn. Engineers who assessed it said the thing would work. Accountants disagreed, and it died.

Parliament finally passed the enabling Bill in 1913, and as documented by Railway Technology, tunnelling started the following year. It was finished by 1917. Then it sat there. The Treasury would not let the Post Office buy operating equipment in wartime, and post-war material prices kept the site quiet until 1923.

The two years it spent as an art vault

A half-built tunnel with no trains in it turns out to be an excellent bomb shelter for antiquities. With Zeppelins and Gotha bombers over London, the British Museum’s trustees decided in February 1918 to move their portable treasures into the unfinished postal railway. One station happened to sit about 300 yards from the museum’s door. Writing in The Art Newspaper, Martin Bailey lists what ended up stacked on that platform: the Elgin frieze, the Rosetta Stone, 118,000 Babylonian and Assyrian tablets and the museum’s entire coin collection.

Tunnel damp is survivable for stone and ruinous for paper, so prints and drawings were quietly shipped off to the National Library of Wales in Aberystwyth instead. Roughly two years later the Rosetta Stone went back to Bloomsbury. Some of what had been sitting underground came up in poor condition, and the repair job that followed pushed the British Museum into setting up its first conservation laboratory.

Twenty-two hours a day

Working the railway was less romantic than the tunnels suggest. Around 220 people ran it, hauling sacks between wagons and platforms while the system operated 22 hours out of every 24, leaving two for maintenance. Trains went flat out through the running tunnels and crawled at about seven miles an hour across the platforms. Gradients did half the work. Stations sat nearer the surface than the track between them, so a train climbed into a platform and braked itself, then tipped downhill on the way out.

Reliability was another matter. RailStaff records that the original fleet of ninety units wore the track down so badly that the whole fleet had to be swapped out within three years.

Why it stopped

Its death warrant was signed above ground. In 1995 a Royal Mail programme called Rail Net pulled mainline mail trains out of central London termini like Paddington and Liverpool Street and sent them to a purpose-built hub at Willesden. Network Rail wanted the platform space back for passengers. The Postal Museum’s own account treats that as the moment the railway lost its reason to exist. Sorting offices had been closing or merging above ground for years, and by 2003 only three of the eight stations were still in use.

Then came the arithmetic. Royal Mail, losing more than a million pounds a day at the time, put the underground option at four to five times the cost of moving the same mail by road. David Chapman, Royal Mail’s London project manager, told reporters the company “simply cannot afford to continue operating an underground railway” that no longer earned its keep.

Nobody outside the company much liked it. Officials at the Communication Workers Union argued the figure was inflated and that the line had been deliberately starved of traffic, run at a fraction of capacity so the numbers would look bad. Members of the London Assembly’s public services committee urged Royal Mail and Transport for London to move fast on returning the line to profit, and floated new cargoes: cash, jewellery, valuables in general. Andrew Pelling, who chaired the committee, made the case for wine. “London is now more a city of drinkers than writers of letters,” he said.

Mail Rail carried its last sacks in the small hours of 31 May 2003, seventy-five years and change after those first Christmas parcels.

What is down there now

The tunnels sat largely undisturbed through the years of mothballing. In 2017 a short loop of them reopened at Mount Pleasant, and as Time Out reported, two battery-powered trains began carrying tourists past the old platforms instead of mail sacks.

Closure rested on a forecast that was largely correct: Londoners were posting less, email had arrived, letter volumes would keep sliding. What nobody in that argument priced in was the parcel, and a city now threading far more delivery vans through the same streets the railway was dug to avoid.