For a building built 50 years ago the BT Tower looks remarkably modern, entering the generous foyer it could be any number of offices that proliferate in this corner of Fitzrovia.

It’s only when reaching the central core you realise the structure’s uniqueness. For running up its centre is that only means of reaching the viewing platform, and the only viable way of escaping in the event of a fire.

[S]eldom seen outside expensive hotels and department stores a lift attendant is on duty as you rise silently at 1,400 ft. per minute as the counter proudly shows. He is also there to help evacuate the building, the only structure in Great Britain allowed using the lift as a fire escape

The reason I am ascending up the most iconic building in London is as a guest of Secret Spaces. It is the sort of access that Google give to their Google City Experts encouraging members to write high-quality local business ratings and reviews on Google+ rewarding members who have left at least 50 reviews to date, and who produce at least five new reviews each month. ­

The program takes advantage of an old Internet rule which states that only a small group of so-called ‘creators’ generate most of the content on the web, while the majority just consumes what others have produced. These requirements are meant to guard against spammers, and others who may be encouraged to write a few reviews in return for free stuff.

After a welcome drink we were given a talk about the changing cities by Leo Hollis, who stated that at the beginning of the century we became 50 per cent urban as a global population, by 2050 Hollis reckons urban population will be up to 70 per cent. From that he extrapolates that by the end of the century virtually the entire world’s population will be urban. So up is the only way to develop our urban living and what better place to present those views that at the BT Tower?

This was followed by a short talk of the Tower’s construction and history by BT’s archivist David Hay, who explained that the Tower is now redundant and used only for promotional work. An amazing image of London taken from the top of the BT Tower has set a new record for the world’s largest panoramic photo. The image shows a full 360 degree view of London in incredible detail.

We arrived at the famous revolving restaurant platform which takes 22 minutes to complete its circuit. It was closed in 1980 due to security fears. At the time many diners said that eating while being spun round was disconcerting. Being the highest building in Fitzrovia it has unrestricted views across London, from Crystal Palace in the south to beyond Wembley Stadium in the north.

As a so-called ‘City Expert’ much of London looks so different from 600ft. in fact I needed help identifying many buildings that I only known from the vantage point of my cab. From the BT Tower London has no edges for, as Leo Hollis predicts, urbanisation stretches for as far as they eye can see.

Pictures: Aiming At The Sky – London BT Tower; BT Tower (Post Office Tower) – London Skyline by Simon and his Camera (CC BY-ND 3.0)

When Google chose a location to launch Secret Spaces, an opportunity to allow access to their favourite places on Google Maps throughout London, they couldn’t have selected a more iconic – or secret – space than the BT Tower.

For if I had written this post 21 years ago
it is quite possible, but in all likelihood
not probable, that MI5 would want to talk to me.

[I]t is hardly the stuff of John le Carré but from the day it was built the Post Office Tower, as it was then, was deemed a State secret. That was until Kate Howie MP, speaking in Parliament on 19th February 1993 spilt the beans about its existence by announcing to the public, and I quote:

Hon. Members have given examples of seemingly trivial information that remains officially secret. An example that has not been mentioned, but which is so trivial that it is worth mentioning, is the absence of the British Telecom tower from Ordnance Survey maps. I hope that I am covered by parliamentary privilege when I reveal that the British Telecom tower does exist and that its address is 60 Cleveland Street, London (Hansard col.632).

Although the core is only 3 metres at its widest point the structure stands 189 metres high – the same as 20 double decker buses parked end to end and unsurprisingly was Britain’s most poorly kept secret.

Londoners were expected not to notice its presence, in fact for many years it did not appear on any map as its location was protected by the Official Secrets Act, even the taking and storing photographs of the building was forbidden.

In a further secret twist Londoners seem to have been unaware of the changes that have been undertaken above their heads as engineers removed the 31 microwave dishes, once used to transmit top secret data across a nationwide network of similar towers.

Right up until the 1980s, the microwave network was responsible for transmitting television signals and other data – some of it military. The arrangement comprised of a link of transmitters, stretching across the United Kingdom from north to south; with towers similar to the London GPO erected in Birmingham (at Snow Hill) and Manchester (in Heaton Park).

Being extremely secure, the system was also known by the codename, ’Backbone’ and, in the event of a nuclear attack, the resilient network would have provided vital communications for the government.

The BT Tower is mostly circular because the designers noted that the only buildings that survived in Hiroshima and Nagasaki were round, with the shape allowing the enormous blast wave to surge round them.

Considering the searing heat and 500mph blast wave unleashed by a nuclear weapon, it is doubtful that any buildings (or indeed people) would have been left standing.

The tower was conceived in the 1950s when broadband microwave technology seemed the best way serve the growing communication needs of the nation. It was designed to exchange microwave radio signals with other similar towers in locations such as Birmingham, Bristol and Portsmouth.

Built in a yard off an existing telephone exchange, it was quite a neat engineering feat. A borehole survey revealed the hard chalk suitable for supporting foundations was 174 feet down, too far to be practically used. Instead an
27 metre square concrete ’raft’ was placed some 8 metres below street level, supporting a 7 metre tall flat topped concrete pyramid, which in turn supported a hollow concrete shaft that forms the core of the tower. Even in 100mph winds it will not sway more than 0.188 metres. Swaying isn’t good for microwave transmission especially in a nuclear holocaust.

In 1962 the GPO Tower (as it was then known) overtook St. Pauls Cathedral as London’s tallest building, that title was briefly snatched away by the newly constructed Millbank Tower which took less time to build, but the title was regained when completed. It held that record until 1980 when the NatWest Tower (now renamed Tower 42) rose above the City skyline.

Known formerly as the General Post Office Tower its presence (or at least its purpose) might have remained a secret but for the fact that a restaurant which revolved every 22 minutes on the 34th floor and operated by the holiday camp king Billy Butin was, at the time, the most fashionable place to dine.

On its opening year in 1963 the Tower attracted 1.5 million visitors and by 1971 had been visited by over 5 million people, it only closed in 1980 amid security fears after a bomb exploded in the gent’s toilet one night causing extensive damage which took two years to repair.

In defiance of the prohibitions placed upon acknowledging its presence it has appeared in BBC’s Doctor Who ’The War Machines’ which curiously does have a ’D’ Notice slapped on it as the YouTube clip has now been withdrawn by the BBC.

A popular backdrop to science fiction films among others V for Vendetta, The Fog, The New Avengers episode Sleeper, The Day of the Triffids and Harry Potter flies over it in a Ford Anglia.

But the all time favourite the Tower is featured in the most famous scene in The Goodies when it is toppled over by Twinkle the Giant Kitten in the episode Kitten Kong.

This iconic location in London now has functions that go beyond it as a building, a restaurant or even a nuclear fallout shelter – it filters broadcast traffic so necessary with today’s need for communication.

This post is based on an article that originally appeared on CabbieBlog in December 2011. Photo: View of the Post Office Tower from London’s Rathbone Street, 1969, JISC Content CC BY-NC-SA.