The producers convinced both the American & British governments to let them use real-life settings as filming locations for the series, including the still-recent American embassy (at Nine Elms) that opened in 2018. Britain allowed filming inside the foreign secretary's office, a rarely bestowed honour for any film or screen production, especially an American one. The one unavailable location was Winfield House, the American ambassador's actual residence. Although it's accurately described as occupying the largest plot of residential land (11 acres) in London aside from Buckingham Palace, the producers used a country house outside the city for filming purposes.
The Lenkov Group is a reference to the real life Russian mercenary Wagner Group and its leader Yevgeny Prigozhin.
Prime Minister Trowbridge's character and ideology is somewhat similar to that of Boris Johnson who was the Prime Minister of the United Kingdom from 2019 to 2022.
It is the second time of Rory Kinnear (Nicol Trowbridge) playing the role of Prime Minister. The first time was in Black Mirror as Prime Minister Michael Callow in the episode The National Anthem - S1 Ep 1.
Production Designers/Set Dressers often make the mistake of not hanging flags properly when vertical. ~26 minutes in, The Union Jack is done correctly, but the Royal Navy White Ensign is not. The Union Jack should always be positioned in the top left canton of viewer, horizontally or vertically.