Artist’s impression of how the space could look [The London Tunnels / Dbox]

THE conundrum of what to do with a Cold War architectural relic in the heart of London could finally be solved as a mega-bucks investment fund unveiled plans this week to convert a labyrinth of tunnels beneath Holborn into a tourist attraction.

Known as the Kingsway Telephone Exchange, the tunnels, which stretch beneath Chancery Lane, cover 8,000 square metres and were originally dug out during the Second World War as deep bomb shelters to protect Londoners from the Luftwaffe.

The plans were to link a series of shelters to tube stations.

But as the Royal Air Force gained superiority, the urgent need for such works lessened.

Instead, the Special Operations Executive, a wartime secret army, moved into the tunnels.

The SOE took the war to occupied Europe with undercover agents and Resistance heroes.

Later the Secret Intelligence Service, MI6, had a base there.

British Telecom used the space to house equipment and telephonists, putting trunk calls through manually before telephone systems became digitised.

And behind security doors the tech systems that kept the presidents of the USA and USSR in touch via a nuclear hotline are still in situ.

But parts of the tunnels – which are as wide as 45feet – remained firmly off limits.

Their existence was always something of an urban myth.

They were kept secret for 70 years under the Official Secrets Act, with public light only being shed on their existence in 2007.

Other highlights include a bar which kept telephone clerks watered. This will reopen, boasting to be the United Kingdom’s deepest underground place to buy a pint.

The tunnels have now been up for sale for 15 years.

Owner Angus Murray hopes to bring some of the magic of Harry Potter to the scheme.

He is looking to partner with big-name Hollywood film firms including the Potter studio Warner Bros and Amazon, which own the James Bond franchise.

Early plans – Mr Murray has yet to apply for planning permission – show the tourist attraction buzzwords including an immersive experience and interactive screens.

The London Tunnels company hopes to bring in around two million visitors a year.

Tickets would cost around £30 per person, raising at least £60million annually.

Mr Murray said his multi-million-pound hole-in-the-ground has as much landmark status as the London Eye, putting £12million of his own money into the project, and describes the plan as offering “block­buster-style experiences”.

The tunnels have a price tag of £40million for preliminary work. A further £100million is predicted to make the tunnels safe and install up-to-date amenities, with a further £380million on attractions.

Architects Wilkinson Eyre Ltd, who worked on the Battersea Power Station project, have been handed the brief.

Mr Murray said: “Where can you get 8,000 square metres of historic novelty in London, which has got a billion dollar reconstruction valuation?”