He presented the Prince Philip Medal for engineering and attended a lunch at The Ritz Hotel in London.

Last night he helped the Queen host a reception at the Palace for education ministers from Africa and Asia.

In between, he worked in his office. An aide said: “He doesn’t like to make a fuss about his birthday. It’s an ordinary working day for him.”

In his honour, a 41-gun salute was fired at midday in Hyde Park by the King’s Troop Royal Horse Artillery and an hour later 62 rounds were fired at Gun Wharf, near the Tower of London, by the Honorary Artillery Company.

There was no sign of the ill health that has plagued the Prince in recent weeks.