London spy sites uncovered
Over the years, London has been a prime setting for the shadowy world of spying. The BBC's security correspondent Gordon Corera goes on a mission to find out how London got its reputation as the "spy capital" of the world.
Most of us are familiar with the modern-day headquarters of the British intelligence services.
The MI5 building at Millbank and the MI6 fortress across the river at Vauxhall are not exactly the most discreet buildings in the capital.
During previous decades the British Secret Service used to be a whole lot more secretive about what it got up to.
During the Second World War, 64 Baker Street was the headquarters of Churchill's "Secret Army", the Special Operations Executive, which he ordered to "set Europe ablaze" with daring assassination and sabotage missions.
These British wartime sites were given a dedicated memorial in 2009, but the buildings where spies were trained and equipped remain almost unknown.
A building at 35 Portland Place was once a top-secret laboratory where real-life 'Qs' created outlandish gadgets - like shaving cream to hide messages in and even exploding rats to conceal in piles of coal.
If you know where to look, London is absolutely full of places that connect to our rich spy heritage.
One of the areas that is particularly packed with spy sites is south Kensington.
The grounds of Holy Trinity Church in Knightsbridge was a location for "dead letter drops" where the KGB used to leave messages for their people.
Mark Birdsall, editor of Eye Spy Intelligence magazine, said: "In the 60s and 70s, this location, and Brompton Oratory, were used by the KGB to deliver packages to agents and handlers.
"It was only revealed when MI6 managed to get one of their top agents out of Moscow and Colonel Oleg Gordievsky exposed these locations.
"In Audley Square there is a single lamppost and the KGB used a chalk mark. Nobody knew about it for years."
For 40 or 50 years the Cafe Daquise in Kensington was visited by some of the most famous spies - including Kim Philby and Donald Maclean - where they would meet contacts and agent handlers to pass on information.
Anna Chapman, who was unmasked as a Russian agent in 2010, had an apartment nearby.
MI6 haunts included the Old Star pub on Broadway and the In And Out officers' club on Piccadilly, which was one of the best places to get a tap on the shoulder from a secret service talent scout.
Boodles at 28 St James Street was a favourite recruiting ground for MI6 officers including James Bond author Ian Fleming, who included the gentlemen's club in one novel, Blades, as M's club of choice.
On any given day, if you take a walk around central London you will probably pass one or two operational sites that are still active, but you will definitely pass half a dozen or more that have been used in the past.
London is the spy capital of the world but then you wouldn't know that.
Gordon Corera's Spy Sites features in Inside Out on BBC One (London), on Monday 7 February at 1930 GMT.