Theresa May has nothing to lose by promising to quit, not least since her party will force her out soon anyway

It is hard to read this prime minister, who zigzags around as she fights for her survival and to keep her divided party in one piece

Why on earth should Theresa May adopt a Brexit Plan B if MPs manage to agree one in their landmark indicative votes starting tonight? The answer is clear. If the prime minister refuses, as she’s threatening to do, the cross-party group of backbenchers driving the process intend to turn the Commons compromise – probably a soft Brexit – into legislation mandating the government to implement it.

Then May really would have a problem.

I am told that Michael Gove tore into his fellow Vote Leave figurehead Boris Johnson at May’s Chequers summit on Sunday, saying: “The prime minister of this country is not allowed to break the law. If a majority of MPs vote for something, she is compelled to obey the law.” The response of Johnson and the other Eurosceptics present was apparently muted. The inscrutable May kept her counsel.

Of course, a soft Brexit imposed by MPs – with membership of a customs union and/or the single market – would be too much for hardline Brexiteers to stomach. Cue more howls of outrage about an unprecedented power grab by parliament making the elected government redundant.

But, as Sir Oliver Letwin, the unlikely shop steward of the backbenchers, rightly pointed out on BBC Radio 4’s Today programme, it's called parliamentary democracy: every week, government legislation is amended by the Commons and Lords. “The courts will enforce the law against the government, as they will against any citizen,” he said.

So Gove is right. Perhaps this is why the penny is finally dropping for the European Research Group (ERG), as more of its members are grudgingly coming round to backing May’s deal. I don’t understand why it has taken them so long. If I were a Eurosceptic (and I’m not), I would have bought months ago Gove’s argument that Brexiteers needed to get their project “over the line” to save it.

Although Jacob Rees-Mogg and Boris Johnson are hinting at supporting the deal, the numbers are not there yet for May. But the parliamentary arithmetic can change quickly, and will do so if the Democratic Unionist Party switches sides. For now, it is holding out, aware that this is its moment of maximum leverage.

Today is backbench power day – and about time too. These indicative votes should have been called by May before she triggered the two-year Article 50 process, in order to see what kind of withdrawal agreement parliament would approve. That might just have bound in some of the 48 per cent, who were ignored by May as she hastily imposed her red lines – still the roadblock today.

Indicative votes should definitely have happened after she lost her overall majority in 2017. Not her style, of course. She continued to behave as if she had a big majority, making inevitable today's impasse between parliament and government. Labour’s Yvette Cooper pleaded with May in 2016 and 2017 to seek consensus, but there was no response.

The prime minister’s refusal to compromise shows in her hesitation about granting free votes when MPs decide which alternative Brexit options they could support. Meaningless, not meaningful. Perhaps the threat of yet more ministerial resignations will make May see sense.

It is hard to read this prime minister, who zigzags around as she fights for her survival and to keep her divided party in one piece. Last week, some cabinet ministers were convinced she would opt for a no-deal exit on 12 April if MPs had not approved her deal. At Chequers, her Eurosceptic guests judged that her no-deal threat was a hoax, as May expressed concern it would jeopardise the Union. She duly highlighted the likely impact on Northern Ireland in the Commons on Monday.

As ever, May sends contradictory messages to different groups: on Sunday, she wanted the Eurosceptics to hear that their dream of no-deal had died, but she would be quite capable of reviving this spectre to present Labour MPs with a final choice between “my deal or no deal.”

No wonder Tory MPs are hoping that May gives a categorical pledge to stand down if her deal passes when she addresses them tonight. Very few of them trust her any longer, so a nod and a wink about not staying forever will fail to persuade enough Eurosceptic opponents to vote for her agreement.

Close allies are urging May to play her last card by setting out a clear departure timetable. Her latest nightmare scenario is that she does that and still loses the next vote on her deal. Yet she has nothing to lose by promising to stand down: win or lose the vote, she will soon be forced out by her own party.