Plaque

English Heritage write: "At various times between 1911 and 1922, flats 53 and 54 - on the building's seventh floor - served not just as Cumming's home, but as the headquarters of the Foreign Section of the Secret Service Bureau."

Designed by Alfred Waterhouse and built in 1884 as residential apartments. The original headquarters of MI5 and MI6. Converted into a hotel in 1971.

MyLondon has some photos of the stunning  interior and reports that at the start of WW2 a tunnel through to Downing Street was built and was often used by Churchill. "The site has been continuously occupied by the National Liberal Club, with strong ties to Prime Minister William Ewart Gladstone".

Everyone loves a hidden tunnel. For more see William Lyttle, the Mole man.