GCHQ has confirmed that an intentionally boring building opposite St James's Park tube station was a secret spy base for 66 years, but has now been sold and is back to being a boring building.
The office block on Palmer Street sits between a pub and a branch of Starbucks, and has frosted windows so you couldn't have a quick shufty and see a spy playing Solitaire.
Unsurprisingly, the secret didn't stay secret for very long — the BBC asked a barmaid at the next-door pub whether she knew what the building was, and she replied "MI6." Close enough.
A nearby barber also commented that it must be "secret service or something" because he'd seen blue-light police cars race down the road to deal with someone loitering nearby. Really subtle, guys.
The building had been in use by the listening post since 1953, as a supplementary site to the big GCHQ-HQ in Cheltenham and a London base for its spies.
The building has now been sold privately and GCHQ has moved out, which is why the agency is OK with admitting its former address. Still, we wouldn't mind a rummage in the bins round there just in case anything got left behind.
Have a look on Google Street View here (from 2008) and see if you can spot any real-life spies:
There will apparently still be a London base for GCHQ, though of course the agency isn't saying where, and we probably won't find out for another 50 years, when they move to a high-tech arcology on the moon.
Main image: Google Maps