More than 300 additional staff were seconded to the department, with the combination of security, protocol and logistics described as the most extensive piece of short-term planning it had faced since Winston Churchill’s state funeral in 1965.
Aside from the practical elements of getting the foreign royals, prime ministers, presidents and governors-general to the capital, the Government also had to pull off the diplomatic masterstroke of keeping certain leaders at a suitable distance.
Ambassadors from North Korea, Nicaragua and Iran were invited, as well as South Korean president Yoon Suk-yeol and Isaac Herzog, the president of Israel, who recently suggested that Iran was leading the global “dark forces of hate”.
Current heads of state invited to the funeral were told they could bring one guest.
In the event, Queen Margrethe of Denmark, who ascended the throne on the death of her father, King Frederick IX, on January 14 1972, attended with her son, Crown Prince Frederik.
The pair were given front row seats in the Abbey, directly opposite the King and Queen Consort.
Australian-born Princess Mary, who married Prince Frederik in 2004 had met the late Queen on several occasions.
Questions over guests of other royal families
A Foreign Office source suggested that in the chaos of the moment, an error was made in suggesting that the guest of Queen Margrethe was also invited to bring a guest.
However, questions remain over why other royal families, including the Dutch, Spanish and Jordanians, had at least three guests each.
Denmark’s Royal House told local news outlet BT: “There has been a regrettable error in the invitation from the British Foreign Office’s protocol.
“It is thus only the Queen and the Crown Prince who, from the Danish side, will participate in Queen Elizabeth II’s state funeral on Monday.”