Updated: 22 Apr 2021, 16:55 MI5 have revealed the “secret to successful spying” in their first Instagram post - but the picture has left Brits scratching their heads. The photo gives a confusing glimpse inside MI5’s top secret HQ, Thames House on London’s Millbank. 5 The photo gives a confusing glimpse inside MI5’s top secret HQ, Thames House on London’s Millbank 5 After 112 years, the Security Service has decided to let the public get a sneak peek insideCredit: Alamy Until now only spies, government officials and a handful of visitors have ever set foot inside, but after 112 years, the Security Service has decided to let the public get a sneak peek by launching @mi5official.