This is the person that could lead a government of national unity

We have reached the point Italy and Belgium know so well where the government breaks down – from corruption, incompetence or sheer incompatibility – and a caretaker administration is needed. Don’t panic. It’s not a walk in the park but nor is it the end of the world.

It works like this. Parliament and/or public opinion finally lose patience with a government which had a narrow basis of support in the first place. Sometimes a dodgy leader goes full rogue – think Berlusconi. Sometimes the gulf between the parties, particularly regional/nationalist ones like the SNP, is simply too great. Sometimes all of the above, as in the person of Matteo Salvini and his Northern League, who and which Boris Johnson and his rump Tory party resemble more each day.

Stability is needed to prepare for elections, or because inconclusive elections have been held and a conventional party government cannot be formed, or not without lengthy horse-trading.

At this point, enter the president of Italy or the King of the Belgians, who instals one of a variety of caretaker or non-party administrations.

Sometimes the outgoing prime minister continues as caretaker; sometimes a more consensual politician does the job; sometimes a respected figure above or beyond politics.

The purest form is the ‘technocratic’ government – Michael Gove’s vision from hell. The governor of the Bank of Italy is a hardy annual on these occasions, if he himself is not being investigated for corruption. In Belgium it tends to be the outgoing prime minister who acts as caretaker – in the case of Yves Leterme in 2010/11 for a record 541 days of ‘interim’ government while a coalition was formed after the 2010 election. Leterme got so bored he announced he would not stay beyond the end of 2011 because he wanted to take a real job.

In our case, an interim government might be needed because Johnson resigns later this month rather than apply for a further extension of EU membership. A variant of this is that MPs at long last pass a motion for a referendum, and Johnson refuses to implement it.

It might also come about because Johnson loses a motion of no confidence in the House of Commons. This could happen, and is now being widely discussed at Westminster, either because he refuses both to send the required extension letter, or implement a referendum, and won’t resign, or because the level of distrust and duplicity is so great that all the opposition parties plus Tories supporting Dominic Grieve and Philip Hammond want him out. So what would happen next?

If Johnson simply resigns, the convention is clear that the leader of the opposition should be asked to form a government. However, Jeremy Corbyn could advise the Queen to send for someone else, maybe as a result of prior inter-party talks. She would almost certainly take this advice if it appears that this putative premier has a Commons majority.

Before the Fixed-Term Parliaments Act (FTPA), either the outgoing or the incoming prime minister could have requested an election, which the Queen would almost certainly have granted in this situation. Now this can only be done with a two-thirds vote of MPs, which means in practice only if Johnson and Corbyn can agree. This is possible, but only after the end of October and the application for an EU extension, which is the very reason why an interim government might be needed. A significant complication is that the FTPA does not say precisely what should happen after a government loses a motion of no confidence. It stipulates that an election will be called automatically if a new government has not secured a vote of confidence from the Commons within 14 days, but it does not require the losing prime minister to resign, nor does it put in place a process for the formation of a new government.

For all these reasons, an interim government is only going to appear credible if there is agreement in the next three weeks on who should head it. Maybe Jo Swinson will ultimately defer to Corbyn, if he promises an immediate referendum and no funny business. Maybe they will agree on a father or mother figure. Ken Clarke and Margaret Beckett are favourites.

The dark horse is John Bercow, whose resignation from the speakership could be accelerated by a week or two to enable him to preside over a referendum government. This idea is gaining traction and would provide the most emphatic non-party leadership to such a government. Of one thing we can be sure: the Queen’s parting with Johnson will not be reluctant. Even Corbyn would be received at Balmoral with greater enthusiasm.