If there is a Conservative leadership election this summer, Boris Johnson will probably win it. A survey of Tory party members last month had him seeing off all rivals in run-off contests — Dominic Raab, Michael Gove, Jeremy Hunt and Sajid Javid.

I understand that Conservative HQ is already divided between pro- and anti-Johnson factions — one working for the incoming prime minister; the other trying to resist his arrival.

So why do the betting markets suggest that there is only a 22 per cent chance that he will be the next Tory leader? That implies a 78 per cent chance that someone else will snatch victory from him, once again, just as he ambles up to the finish line.

The key is the word with which I started: “If”. If there is a vacancy this summer, Johnson has a good chance of becoming prime minister. And Theresa May is being jostled towards the exit, rather in the way I once saw an obnoxious drunk man being ejected from a crowded Tube train. No one said anything, they just turned their shoulders until he was pushed out.

But May is not going yet. This week she has bought herself another week. She met Sir Graham Brady, the chair of the 1922 Committee which represents Conservative backbench MPs, and offered to meet his executive next week to discuss the timetable for her departure.

Last night she bought herself another day. The meeting, which was going to be on Wednesday, is now going to be on Thursday morning. I have a vision of the prime minister in the New Yorker cartoon by Bob Mankoff, on the phone to Sir Graham as she consults her desk diary: “No, Thursday’s out. How about never — is never good for you?”

Presumably, though, the meeting will take place on Thursday, and Sir Graham said last night: “It would be strange for that not to result in a clear understanding at the end of the meeting.”

Well, some strange things have happened in politics recently and we shouldn’t be surprised if May simply repeated her position. Her spokespeople keep calling this “a very generous and bold offer”, as if it is really gracious of her to stick around while her party makes up its mind: she’ll stand down if we leave the EU; she will stay only as long as Tory MPs want her to; and she won’t lead them into the next election.

The only question, therefore, is whether a majority of Tory MPs want to keep her in the post. If the 18-member executive of the 1922 Committee is not satisfied by her answers on Thursday and suggests rewriting the rules to allow a challenge to her leadership, that still requires 157 Tory MPs, one more than half the total, to vote her out.

Only then does Johnson as prime minister become likely. Despite having become a tired old caricature of himself, he has enough support among MPs now, I think, to guarantee a place in the final two, from whom party members will choose. He has been in the tea room and the Portcullis House cafe, chatting to colleagues about their hobby horses.

If they finally want to test the proposition that no one could be a worse prime minister than Theresa May, Johnson stands ready to offer a live experiment. And that, as Johnson broods over his plan for government, is his dilemma. The one thing worse for him than having the cup of victory dashed from his lips again would be to win.

He would then become prime minister with Brexit unresolved and the EU waiting to hear what his plan would be by 31 October. So far as can be deduced from his weekly column in The Daily Telegraph urging the nation to buck up and look on the bright side, his plan is to renegotiate the withdrawal agreement and, when the EU says no, to leave anyway.

But one thing we know from the drama of Brexit votes in the House of Commons is that parliament will not allow a no-deal exit. It would legislate to try to prevent it and, if that did not work, my view is that it would depose Johnson and install David Lidington — for example — as temporary prime minister for the purpose of agreeing a further extension of EU membership.