It could be all over on Monday or the Conservatives may be about to mesmerise the nation with another round of vicious infighting.

The Conservative Party rules can’t be changed. They are that Conservative MPs draw up a shortlist of two candidates from their number.

The 180,000 paid-up and unelected party members then choose between them. Less than half of those eligible to vote actually voted for Liz Truss last time but they still overruled the MPs’ preference and saddled the nation with a prime minister who lasted less than 50 days.

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Sir Graham Brady and the executive of the 1922 Committee of backbenchers have done what they can to try to stop it happening again by changing the way MPs draw up the shortlist. It is possible that the MPs will present the membership with a fait accompli early next week.

After the bumpy ride for the country and their party under Boris Johnson and Liz Truss, senior Tory backbenchers have done what they can to ensure an orderly transition to an orthodox candidate: most likely Rishi Sunak or Penny Mordaunt, who were the runners-up in the last contest which, amazingly, elected Ms Truss less than two months ago.

As things stand, however, there is a chance that these best laid plans could go awry, resulting in Britain ending up with another “disrupter” prime minister drawn from an unrepresentative band of populist libertarians.

How will Tories pick the new PM?

The ’22 have set the threshold for nominations high. To enter the contest, a candidate will need to gather written backing from 100 fellow Tory MPs over this weekend. That is five times higher than the 20 required last time and has the desired effect of limiting the field to a maximum of three candidates since there are only 357 Conservatives in the Commons.

Nominations will close at 2pm on Monday. MPs will then vote, with the results declared at 6pm. Theoretically, that may not be necessary. It is possible that only one candidate – Rishi Sunak, the runaway favourite – will get enough nominations. He would then win by a walkover, similiar to the way Gordon Brown took over the premiership from Tony Blair.

Nominating someone is more potent than just voting for them. Remember the charity nominations Margaret Beckett and other “morons”, her words not mine, gave Jeremy Corbyn so he could run. This time MPs might decide that Mr Sunak is going to win anyway, so for a quiet life and possibly currying favour with the new boss they could give him a key to No 10.

But in the final round this summer, Mr Sunak led with 137 votes, to 113 for Ms Truss and 105 for Penny Mordaunt. Ms Mordaunt wants to run again and is scrabbling for her base to nominate her. In polls this summer she was more popular with Tory voters than Mr Sunak. She would prefer a straight fight with Mr Sunak, whether that comes about because only she and he are nominated or because they beat a possible third candidate in an initial vote.

If there are two candidates left for the membership to choose from, there will be an online ballot of the membership next week, with the result declared on Friday. Before that, the ’22 have already said that there will be “an indicative vote” between them first by MPs. The purpose of this is to send a powerful and unambiguous message to the membership about whom MPs want as leader. In choosing Ms Truss last time they went against the MPs’ first preference of Sunak.

If Mr Sunak and Ms Mordaunt are the final two, they could still take the decision out of the membership’s hands by agreeing that one who has least backing from MPs withdraw in favour of the one with most, allowing him or her to become prime minister. They would also both commit in advance to serve in the same cabinet and to keep Jeremy Hunt as chancellor .

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Will Johnson derail the smooth transition?

Such a smooth transition would be derailed if there is a third candidate with 100 nominations.

All eyes are on Boris Johnson, who is said, like Donald Trump, to want a comeback. If, and it is a big if, he gets on to the starting grid, there could be a stampede of MPs who might decide he looks like a vote winner and put him into the second round against either Ms Mordaunt or Mr Sunak.

His chances of victory and re-election by the membership would be very high. He is popular and he is the only candidate who can claim a personal mandate, having led the party to victory in the 2019 general election.

But, but, but.

Tory MPs and cabinet ministers turfed out Mr Johnson this summer for serial dishonesty and sending others out to lie on his behalf. Jacob Rees-Mogg, Nadine Dorries and a few diehards may be calling on him to return but he has never been loved by the rank and file of the parliamentary party, who control the nominations. Nor does he fit snuggly with the libertarian, UKIP-style entryists of the European Research Group, who are now fighting a rear-guard action to preserve their influence in the party.

There are obvious efforts by Johnson supporters in parliament and the media to talk him up this weekend. But his shooting star support from some MPs could easily plateau short of 100 nominations. If so, having drawn attention to himself yet again, Mr Johnson would most likely return to his less demanding, more lucrative exertions on the US lecture circuit.

Could an unlikely outsider emerge?

If it is not Mr Johnson, someone else could emerge as the third challenger.

Suella Braverman fancies her chances and her sacking as Ms Truss’s home secretary positions her to rally the right. Kemi Badenoch also has high ambitions.

Fortunately for Ms Mordaunt or Mr Sunak, Jeremy Hunt and Ben Wallace have both ruled themselves out of the race. It is unlikely anyone else would be able to muster 100 nominating signatures.

Shell-shocked Tory MPs do not want to take the risk of taking a punt on another incoherent or incompetent leader. They want a well-known figure with a proven track record to steady the ship.

In the ultimate reckoning, this is likely to count against Ms Mordaunt. At 49, she is older than Mr Sunak, 42, and has been in parliament five years longer, since 2010. But she has served barely two years as a cabinet minister.

Mr Sunak by contrast has three years in cabinet under his belt, two of them as the chancellor who piloted the economy through COVID.

MPs have the future of the nation in their hands. One option would be to open the door to the return of the discredited individual they kicked out a few months ago. Or they could shut him out for good and opt for a technocrat.