Every ambassador to Britain from a non-commonwealth country, whether superpower or tiny principality, carries the title “ambassador extraordinary and plenipotentiary to the court of St James’s”. On taking up their posts, they are driven through the London traffic in horse-drawn carriages to present their credentials to the Queen. Ambassadors for Commonwealth countries don’t share these gilded titles – they are known as mere high commissioners – but their coach to the palace is pulled by four of the Queen’s horses rather than two.

There may be general equality of etiquette, but are some diplomats more equal than others? The major powers maintain industrial-size missions in the capital – US ambassador Robert Holmes Tuttle, for example, is in charge of 440 diplomatic and 330 support staff in his vast embassy-fortress in Grosvenor Square, Mayfair. Japan has 140 staff in its Piccadilly pile, and France more than 60 diplomats and an ambassador’s residence in Kensington that once belonged to the 10th Duke of Marlborough.