On the death of George V in 1936, grave difficulties arose. Edward VIII showed he was unwilling to make the sacrifices of personal inclination which are required of a constitutional monarch. His insistence on marrying Wallis Simpson, a twice-divorced American, led to the Abdication crisis. Had he wished merely to retain her as a mistress, matters would not have come to a head so quickly. But Baldwin, as Prime Minister, mobilised the Establishment and insisted that “in the choice of a queen the voice of the people must be heard”.

Here, one may note, was a chance to get rid of the monarchy altogether. James Maxton, an Independent Labour MP, duly proposed in Parliament that Britain should become a republic. His motion was defeated by 403 votes to 5. Neither the ruling classes nor the people wanted a republic. What they wanted was a dutiful monarch, and in George III that is what they got.

Baldwin described the monarchy as “the guarantee against many evils”. It remains one of the greatest, though least observed, checks on arbitrary power, for the king or queen occupies the space a dictator would need to occupy. Because it is unthinkable in Britain to push the monarchy aside, tyranny itself becomes unthinkable. In countries where the monarchy was overthrown — France in 1789, Russia in 1917, Germany in 1918 — tyranny was not unthinkable. Our hereditary umpire is not just decorative: she stops the players from getting out of hand. When Jeremy Corbyn declined to sing “God Save the Queen”, he did himself great harm, and her no harm at all.

It is true that the Queen has no power to run the government which is carried on in her name. Her ministers do that, and take the blame when things go wrong. The prime minister exercises an impressive range of royal prerogatives. Tony Benn used to complain about that, and I confess I thought he was wrong-headed. But it now occurs to me that he was on to something. George III tried, by the exercise of patronage, to control Parliament. So does David Cameron. I wonder if Eric Nelson could be prevailed on to write another book, in which he examines whether Cameron has become, in reality though not in name, an elected monarch.