Ask a Tory backbencher or minister when Theresa May should stand down, and the answer depends heavily on who they want to succeed her. Hardline Eurosceptics can’t wait to force May out of Downing Street. They have every incentive to inflict a fourth Commons defeat on her Brexit deal next month; they hope to install one of their tribe in her place to complete the Brexit process.

The latest threat to May is a plan for grassroots Tories to call an emergency meeting of their body, the National Convention, to pass a vote of no confidence in her.

An early contest would suit former ministers Boris Johnson and Dominic Raab, who would be less tainted by the government’s failure to deliver Brexit. They might feel free to make unrealistic demands for the EU to change the Irish backstop, or pledge to leave without a deal, even though that course is opposed by the majority of MPs.

Conversely, cabinet ministers with an eye on May’s job would rather delay a leadership contest. There are eight of them at the last count – Sajid Javid, Jeremy Hunt, Michael Gove, Matt Hancock, Amber Rudd, Andrea Leadsom, Liz Truss and Penny Mordaunt. Most of them argue the six-month delay to Brexit does not leave long enough for a leadership election, and that the right time is after the UK has left, so the focus can switch to domestic policy. Which, roughly translated, means they would rather take over when May has finally found a way out of the Brexit mire, so the mud sticks to her rather than them.

May has no intention of quitting until she wins Commons approval for a deal. But events could soon spiral out of her control. She is braced for heavy Tory losses in the council elections on 2 May and the European parliament elections on 23 May, a meeting with the voters she is unlikely to avoid.

If May manages to hang on until the autumn, it could be one of the longest leadership elections in recent history. The jockeying for position by cabinet ministers is not even disguised now. While the prime minister is on a short break in Wales, potential successors are displaying their wares.

The person who could decide the Tory contest is Rudd, the work and pensions secretary. She is being courted by other candidates as her endorsement would bring with it other MPs in her One Nation group. On Tuesday, Rudd said it was “entirely possible” she would run, but I doubt she will. I suspect the die was cast when she discussed her plans with close allies before penning a joint newspaper article with cabinet colleagues David Gauke and Greg Clark, which defied May by opposing a no-deal exit. Rudd knew that proposing a Brexit delay would make it very difficult for her to win the leadership. Refreshingly, she put the national interest above self-interest.

She does not rule out backing Boris, although that would be harder before Brexit has been resolved, given the differences between them on the issue.

I detect an improvement in Johnson’s prospects since May failed to take the UK out of the EU on 29 March. The Tories have slumped in the opinion polls since, as Leave voters desert them. In turn, this has encouraged some Tory MPs who do not love Boris to reappraise him, and conclude he might offer their best hope of defeating Labour.

Crucially, his enemies may now find it harder to conspire to keep Johnson off the shortlist of two names chosen by Tory MPs, who then go into a ballot of the party’s 120,000 members. If he makes the run-off, Boris will be very difficult to stop.

Although May will keep her counsel about who should succeed her, it’s a safe bet she would not want it to be Johnson. Yet she may depart with her party in such dire straits that it makes a Boris premiership more likely.