Queen Wilhelmina of the Netherlands had Her Secretariat in this house, 1940 - 1945.
Site: Queen Wilhelmina (1 memorial)
SW1, Chester Square, 77
The website of the United Kingdom NL Embassy wrote that the Dutch Queen's first home in London was at 82 Eaton Square but then "The Queen stayed {in Chester Square} during the Blitz, and would only go to the refuge shelter in the back garden during heavy bombing. Prince Bernhard’s office was on the ground floor of the building. He met Erik Hazelhoff Roelfzema, a Dutch RAF pilot, here, where they discussed the Dutch espionage service. This service (‘Contact Holland’) was from then on led by Erik Hazelhoff Roelfzema and Peter Tazelaar from the residence’s garden house."
It's a bit confusing because that site also said "When the bombardments during the Blitz became too dangerous, the Queen moved to Stubbings House in Maidenhead. She moved in on 30 October 1940 and stayed until the beginning of 1944." Also the Queen and the Prince must also have at least visited Claridge's quite often because they are reported as seeking shelter from the bombing in the basement.
That website has now changed to be:
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