Theresa May decided to pull the parliamentary vote on her Brexit withdrawal agreement because she knew she would lose. She has been humiliated by her own MPs. It is staggering that this defeat only became obvious to her after it had been clear to everyone else for weeks. In the end, she chose to run rather than stand and fight for what she had agreed with European leaders. Mrs May is not saving her leadership, she is devaluing it to the point of worthlessness. The prime minister has no one to blame but herself for this mess. In the last two years the government has devoted itself to leaving the European Union in a manner consistent with Mrs May’s obsessions – primarily controlling immigration. Her resulting withdrawal agreement has been rubbished by her own unruly troops. They will not be easily instructed to march in a different direction.

The prime minister is trying to buy herself time by getting Brussels to accept some tweaks in her Brexit deal over the Northern Ireland backstop as a means of persuading some doubters to vote for it. These will be cosmetic, as EU leaders say there can be no further renegotiation of the terms of the UK’s departure.

The threats to Mrs May are multiplying. In parliament, the prime minister foreshadowed a constitutional trial of strength in a furious exchange with the Commons speaker, John Bercow. Mr Bercow rightly called for MPs to be allowed to vote on postponing the Brexit debate. In rejecting this, the prime minister continues to treat parliament with contempt.

Crises of this nature are only resolved in line with a Commons majority. Mrs May’s actions invite MPs across parties to coordinate with one another so they make the conduct of the government impossible unless ministers bow to their will. It is important to note that Mrs May’s deal, even in its refined form, will garner less support in the Commons than either another referendum, in which the risk of the option of a catastrophic “no deal” is endorsed by a weary public, or some variant of the Norway deal, in which we give up sovereignty for economic stability.

The prime minister wants to play for time, saying only that the vote on her deal, replete with reassurances, will be held by 21 January – the last possible date to do so. If dodging a defeat becomes the only way for Mrs May to survive, then the indications are that she will delay a vote until the last possible moment. This is playing politics with the nation’s stability. It ill behoves any prime minister to be so cavalier about such a serious issue.

Her decision to stay on is one based on her own self-interest and that of her party rather than the country. The prime minister is now a diminished figure, with her authority draining away on the most important issue facing Britain. It is galling to hear her claim that the 2016 referendum vote was a cry for help from left-behind Britain when it was Tory austerity that hollowed out deprived regions. Since then, Brexit has immobilised the government, leaving it unable to deal with these problems.

Mrs May might claim that she lives to fight another day. But given that the leadership is on the run from the hard Brexiters, she lives on only as a political zombie. Ensnared by her own convictions, she has resorted to dilatory tactics because she has belatedly realised the full weight of their burden. When, at last, she has been forced to recognise this, she found herself alone and politically friendless in a party that prefers accommodation of its prejudices to political calculation – let alone what is best for this country.