May began this week on Radio 4’s Today Programme doubling down on her Chequers plan. In the other corner, (via his Daily Telegraph column) Boris Johnson claimed the plan would mean ‘acquiescing in foreign rule’.

Meanwhile, for Labour, Shadow Foreign Secretary, Emily Thornberry has said her party will vote against whatever deal May comes back with.

By characterising the deal as ‘her way or the highway’, May is clearly confronting her opponents with the prospect of being blamed for the UK crashing out of the EU next March with no deal and no transitional arrangements in place. The question is, do they care? Will an alliance of Tory rebels and Labour MPs really be prepared to vote down a deal, risking chaos?

The numbers are very tight. With a working majority of just 13, in theory an alliance of only seven rebel Tories along with the combined opposition parties could defeat the ‘meaningful vote’ motion the Government is committed to bringing before the House of Commons.

Looking through the list of known Tory European Research Group members and supporters it’s not hard to come up with a list of seven or more hard-core opponents to the Chequers deal who might well favour taking the country to the brink, rather than endorse what they see as ‘the worst of all possible worlds’.

And, of course, whatever deal May manages to get from the EU is likely to go somewhat further than her Chequers plan in the Commission’s direction, given the nature of such negotiations.

On the Labour side, the prospect of a defeat precipitating a Tory leadership crisis and an early General Election would seem all too tempting.

The remainers among Labour MPs, who comprise the vast majority of the Parliamentary Party, don’t like Chequers because it falls short of their long-term aspiration to stay within the customs union or within the EU overall.

Like their Tory counterparts, Labour’s leavers view Chequers as a sell-out and would also be comfortable to oppose it. One result of May’s resolve may well be to unite Labour MPs in a way that they have been unable to do themselves ever since Jeremy Corbyn became leader.

The fragility of May’s position in Parliament will be tested more than once: the motion on the Withdrawal Agreement itself and then the further primary legislation needed to give it effect.

Amendments to either the motion or at any stage during the subsequent passage of the legislation could effectively hijack May’s deal.

One course of action open to MPs, which some are actively considering, is tabling amendments which make either the motion to approve the agreement or the subsequent bill subject to a further referendum of the people of the UK.

If push comes to shove and May is really forced to choose between ‘her way or the highway’, the promise of a second referendum could be a possible way out.

What of the longer term Free Trade Agreement? At this stage most observers believe that the best on offer this side of Christmas will be a formal Withdrawal Agreement (covering the UK’s financial commitments, the position of EU citizens and the Northern Ireland border) and then a high-level statement of intent around future trading arrangements between the UK and EU, subject to negotiation during the period that the UK is in transition up to December 2020.

But some commentators (including in this latest Institute for Government report) are saying that even this prolonged timetable is highly ambitious given the wide-ranging nature of the agreement that will need to be reached. So it is possible that a further extension of the UK’s transitional arrangements will need to be sought.

The multi-billion dollar question as we go into this party conference season is: are May’s opponents within the Tory party really committed to killing off her plan, aware that the consequences of this could be both an end to her premiership and a no deal Brexit?

With Labour’s position hardening, it is a question that the seven or so potential Tory rebels who could decide the matter really need to answer.