Ostensibly, Theresa May went on BBC Radio 4’s Today programme on Thursday to address all the listeners. In reality, however, her aim was to reach an audience of fewer than 200. The people she wanted to influence are the Conservative MPs who hold her government’s future in their hands next Tuesday in the votes on her Brexit deal.

Mrs May’s pitch was narrowly focused. She was now “talking to colleagues” about ways in which parliament might be involved in activating the Northern Ireland backstop – a clause in the withdrawal agreement whose purpose is to prevent the return of a physical border in Ireland following the post-Brexit transition between March 2019 and December 2020. MPs might, she suggested, be able to choose whether to enter the backstop or extend the transition a bit further. Translated, this meant that Mrs May wanted to appear open to marginal changes in her Brexit deal as a means of persuading some doubters to vote for it next week.

It was abjectly thin stuff. It was not anything that can plausibly be presented as a tweak, let alone a renegotiation, of the Brexit deal – because such a thing is not on offer. In fact, these apparent concessions are already part of the Northern Ireland protocol in the withdrawal agreement. The government’s explanatory document on the agreement, published last month, says as much. It says, in paragraph 157, that Britain could enter the backstop or opt for a transition extension: “This would allow the UK government, with an appropriate role for parliament, to consider the right approach in the national interest.” Mrs May, in other words, used her interview to offer a nicely wrapped version of something that has already been agreed.

Logically, this might seem to mean that Mrs May will not succeed with this approach to her backbenchers. This is, though, to underestimate the pressures on Tory MPs. Ordinarily, they – and their local activists – want to support the prime minister and her government. It remains the case that a minority of Tory MPs are so entrenched in their views for or against Brexit that their votes against her deal were locked down from the start of the whole process. That is why, until this week, Mrs May won almost every key vote.

Her problem now is with the backbench MPs who dislike both the deal itself and the fuss it has caused, and who have persuaded themselves, looking at the parliamentary arithmetic and at the hints that the deal could be tweaked, that they have permission to vote against the deal without bringing the government down. Pressure on these MPs will tighten over the weekend and right up to the vote on Tuesday. On Thursday one former pro-European Tory critic, Antoinette Sandbach, agreed to back Mrs May with the words: “It may not be perfect but it is a good deal.” She is very unlikely to be the last to change her mind. But the larger problem for Mrs May is that she is fighting on two fronts, against anti-EU fanatics who abhor every continuing post-Brexit tie with Europe, and against pro-EU remainers who see a chance of overturning the 2016 referendum.

Mrs May’s concentration on the backstop in her interview confirms that ensuring the current frictionless border in Ireland has become the pivotal issue in the Brexit deal endgame. Jeremy Corbyn makes this case in his Guardian article today. The usually tight-lipped Tory backbench chair Sir Graham Brady said the same on Thursday to the BBC.

If nothing else, this is an example of English Toryism’s chickens coming home to roost. The leave campaign in England utterly ignored the warnings in 2016 from Sir John Major, Tony Blair and others about the disruptions that Brexit could bring to Ireland. Northern Irish voters, where a majority chose to remain, could not be so dismissive. But Mrs May then ignored warnings that a post-election deal with the DUP – a party fundamentally out of step on Brexit with majority opinion in Northern Ireland and the Republic – would come back to haunt her. Not for the first time in British history the Tory party is again faced with a choice between protecting its narrow interests and what Sir Robert Peel, at the height of the Corn Law crisis, called the need to “understand this Irish case”. Peel did. Mrs May doesn’t.