Boris Johnson makes the case for our constitutional monarchy. Donald Trump makes one for a written constitution. How?

Seeing Mr Johnson’s arrival at the King’s Coronation prompted the thought that, with all its oddities, a constitutional monarchy remains the least bad option for our head of state. We could cut its costs, if we want. We could scale it down. We could reduce still further its constitutional powers (as in New Zealand). It could keep its role as a national symbol. For that, its hereditary background and tradition is a plus, not minus. Mr Johnson’s helpful role in this argument is that he reminds us of the risks of the alternative. We have shown that he is the sort of person we might elect as President. Arguably he would be better at being President than at being Prime Minister – more theatre, less detailed work. But I don’t find it a pleasing prospect.

Elected presidents, even if less inflammatory than Mr Johnson, would inevitably be divisive: it is probable that nearly half the electorate would have voted against the intended embodiment of national unity. Ireland’s head of state has roughly the same function as ours. For over 50 years, the incumbent was a not-too-alienating (ie boring), retired second-rank politician. A series of entertaining political accidents in 1990 overturned this pattern, since when the parties have nominated more interesting, less political and more unifying candidates. But I doubt that we would do much better than the Irish in shortening the 50-year path to their now quite good system. And the Irish didn’t have the option of our traditional model.

Mr Trump’s contribution to our political debate is different. His reaction to losing in E Jean Carroll v Donald J. Trump was to rail against the courts, saying that something must be done about them. In the US, in practice, there isn’t much he can do about courts, even if he becomes President again, though he can appoint judges, usually with some balancing safeguards. He can do even less about state courts. When Mr Sunak or Ms Braverman threaten to do something about English courts, there aren’t many limits to what they can do if they have the House of Commons’ backing. They could do something about the Scottish courts too – or the whole of the Scotland Act.

Mr Trump highlights our system’s fragility, illustrated by recent Whitehall minsters’ unprecedented disregard for the conventions underpinning our unwritten constitution. Some safeguards went with the EU’s Charter of Fundamental Freedoms. Ministers openly talk of abandoning the older protections of the European Convention on Human Rights. Having weakened respect for conventions, it is hard to recreate this respect. The unelected, and therefore easily undermined, House of Lords is almost the only brake on this constitutional battering-ram. Even they can generally only tinker or delay. And a likely new government, even one more likely to respect conventions, looks likely to make the second chamber elected. This would create a more disciplined, partisan House, increasing risks that one party could control both Houses. Then we really would be at the mercy of a ruling party.

George Fergusson is a retired senior diplomat