There’s an interesting story behind this door:

Named after this house is the Chatham House Rule, used around the world to ensure free and open debate.  The rule reads as follows:

When a meeting, or part thereof, is held under the Chatham House Rule, participants are free to use the information received, but neither the identity nor the affiliation of the speaker(s), nor that of any other participant, may be revealed.

It may be invoked at meetings to encourage openness and the sharing of information.

Chatham House, where the rule was established in 1927, is based in the heart of London, in St James Square.  The building was home to three Prime Ministers (William Pitt the Elder, Edward Stanley and William Gladstone) before being gifted to what was then the British Institute of International Affairs in 1923.