Imagine for a moment that Boris Johnson had gone down with the Coronavirus at the end of last week.  As he and other Ministers were debating whether or not to impose a national lockdown.

Even then, he could have carried on leading the decision-making through what he calls, in his video announcement, “the wizardry of modern technology”.

And this is not the end of last week.  At the moment, the most important Government action is the rolling-out of testing to the general public, ventilators to the NHS and equipment to healthcare staff and others.

That can be chased up via the four Cabinet committees chaired by Matt Hancock (healthcare), Michael Gove (the rest of the public sector), Rishi Sunak (economy) and Dominic Raab (international).

With no major decision pending, the Prime Minister can let this process roll on without having to hand over to Dominic Raab, the First Secretary of State.

Johnson has a robust constitution and will not want to let go of anything until or unless he absolutely has to.  And the symptoms of the virus can be, to borrow his own word, “mild”.

If they become more severe and if his illness stretches on – a fortnight is apparently not uncommon – then the Foreign Secretary will take over for the moment.

That would not be a smooth process at the best of times, and Raab is not formally number two in the Cabinet pecking order: that’s Rushi Sunak, followed by Raab, then Priti Patel, then Michael Gove.

The Government would probably run in these circumstances as a kind of Raab-Sunak-Gove triumvate, but let’s not get ahead of ourselves.

Those with whom the Prime Minister has been in contact will want to get tested if they get ill, but there will be no evidence that he has been the source of the infection.

After all, he himself will have caught it from a second party, others who work in Downing Street also have the virus, and estimating whether A got it from B rather than C in these circumstances is a mission impossible.

It goes almost without saying that it was essential to test the man in charge of our national response.  We send Johnson best wishes for a speedy recovery.