Boris Johnson has been moved to intensive care after his coronavirus symptoms worsened and has asked Foreign Secretary Dominic Raab to deputise “where necessary”. But what would happen if the prime minister were to be incapacitated?
The formal rules for what should happen if such situation arises are unclear – a consequence of the UK’s unwritten constitution.
But we do have some ideas about how things might play out. The cabinet manual is the closest thing we have to a document which sets out the role of the prime minister.
Mr Raab, as first secretary of state, is the designated stand in. So if the official position changes, with the prime minister formally relinquishing control, he would take over in the first instance.
What would that mean though? There are various things that only the prime minister is authorised to do.
Some of these could be taken up by Mr Raab without too much problem. For example, he could make recommendations to the Queen on appointments to the senior judiciary and to high-ranking positions in the Church of England.
But it is harder to imagine him conducting a reshuffle – even though, formally, it seems he ought to have that power. And things seem to get even less likely as we get to the more significant prerogative powers.
In practice any major decisions would probably be taken by Mr Raab in consultation with the cabinet or, where appropriate, the cabinet secretary and other senior officials.
A tricky example would be the authorising of military action. In an urgent situation he might have to do that – but presumably it would be agreed first by other senior cabinet ministers.
Another difficult question would be the letters of last resort that the prime minister writes for the nuclear submarines, giving the commanding officers instructions about what to do in the event of a deadly attack on the PM.
It is hard to see that Mr Raab would be asked to write them unless Mr Johnson was going to be incapacitated for a long time – and maybe not unless he actually stepped down as prime minister.
In those circumstances, or if the prime minister died, we would expect the Queen to ask Mr Raab to form a government – at least on an interim basis – unless the cabinet put forward someone else.
The expectation is that he would be in place until the Conservative Party appointed a new leader.
According to the Institute for Government think tank, prime ministers continue in office unless they resign or die.
It adds: “While political parties usually have the ability to appoint an ‘acting leader’ if the leader resigns or is incapacitated, there is no formal ‘acting prime minister’ role. He or she would be prime minister until they chose to resign or if their cabinet forced them out.”