It was founded 112 years ago amid escalating tensions with Imperial Germany.
Since then, MI5 s spies have worked in the shadows to snoop on targets, foil bomb plots and keep leading politicians informed.
But now, the domestic intelligence agency, which is also known as the Security Service, has said goodbye to secrecy and revealed the inside of its former Mayfair base for the first time.
Posting the for your eyes only pictures on it s Instagram account, the spy agency said: More than 25 years after MI5 left the building for the last time, we re now pleased to be able to share some rare images of our Curzon Street office, the home of MI5 between 1977-1994.
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