It was when cabinet ministers were asked to join a conference call on Monday evening with Mark Sedwill, Britain’s top civil servant, that they knew the coronavirus crisis was taking a dark new turn. “It’s never good news when you get a call like that,” said one minister.

Sir Mark’s confirmation that UK prime Minister Boris Johnson had gone into intensive care meant that the government, already struggling to keep up with the virulent spread of the disease, now had to adapt to a situation where its leader was himself stricken by the virus.

Mr Johnson’s instruction that Dominic Raab, foreign secretary, should deputise for him “as necessary” put the spotlight on Britain’s notoriously opaque constitutional arrangements and how its government should function in an emergency.