IT WAS the Royal Mail’s deepest secret: a miniature underground railway that takes sacks of post across London in half the time of a van.

Now, after 75 years of service, Mail Rail, the underground postal system stretching across seven miles of the city, is to be put up for sale.

Businesses around the capital might well be enticed by the benefits of a first-class delivery service that is swift, secure and impervious to traffic jams or the congestion charge. Plans are already afoot to see the railway, thought to be worth more than £15 million, redeveloped as a way to transport goods to London’s busiest streets and shops.

Mail Rail, which is being mothballed in an economy drive by Royal Mail, runs for 23 miles between Whitechapel and Paddington, including stops at Mount Pleasant and Oxford Street, and carries 34 trains along its electrified tracks.

When not delivering post, the service has also appeared in films — including a role as a secret railway inside the Vatican in the Hollywood film Hudson Hawk — and provided secure storage for many famous artworks during the Second World War.

As Mail Rail prepared for its final week of service yesterday, employees said that a unique asset deserved a long future serving the city.

After 37 years working as a Mail Rail engineer, Michael Frampton, 53, was completing his final shift yesterday after taking redundancy along with several dozen colleagues. Of Mail Rail’s 76 workers, most are being laid off or retrained for other roles.

“It is really very sad because it has been such great fun to work on, like a big boy’s plaything,” he said. “But it is the only way to get a bag of mail from one side of London to the other in under 30 minutes. It really deserves a good future. If I was in charge I would set it up as a white-knuckle ride, but I’m sure it will find a more practical use.”

The driverless miniature trains, each 28ft long and 4ft high, were still hard at work 70ft under London yesterday, transporting bags of mail from Mount Pleasant to Paddington. The service, the only remaining underground mail railway in the world, shifts 3.4 million letters a week, half the number it carried 50 years ago.

Andrew Pelling, chairman of the London Assembly’s public services committee and author of a report into the future of Mail Rail, said he hoped that an entrepreneur would see the value of “the ultimate train set”. Development agencies were considering a range of uses, including delivery of alcohol, precious metals to Mayfair’s jewellers and all manner of goods to Central London’s department stores.

As it runs to Paddington, which links directly to Heathrow, Mail Rail could also be used as a secure link for important air freight, he said.

“It is one of London’s important assets. It is a service that you can absolutely rely on,” Mr Pelling said.

Mail Rail was first devised in the 19th century as London’s roads became increasingly congested. Work on a network of nine stations from Paddington to Whitechapel, including sites at Liverpool Street, Oxford Street and near the Old Bailey, began shortly before the First World War and was completed 12 years later.

Five stations have closed over the years, most recently Whitechapel in March, as the cost of running the postal network grew.

James Taylor, a spokesman for Royal Mail, described the closure of Mail Rail as a huge shame brought about by financial and logistical factors. He said that Royal Mail was in discussion with several interested parties about the network’s future.

“Our major post offices have moved over the years, and Mail Rail can no longer serve many of them directly. Also we realised that operating the railway was costing five times more than using extra lorries.We really feeel it has huge potential. Sadly it is just no longer right for us, but I am very hopeful it will find a new role.”

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