Has prime minister just signed her own warrant of execution?

The prime minister might have been a bit too clever when attacking Jeremy Corbyn's and Labour's opposition to her Brexit deal.

Some four hours in to her 14-hour flight to the G20 leading nations' summit in Argentina, she told journalists:

"What they are doing is advocating rejecting the deal we negotiated with the European Union without having any proper alternative to it.

"They say they don't want 'no-deal', but by appearing to reject a temporary backstop they are effectively advocating no-deal, because without a backstop there is no deal."

So, she is accusing Labour of ushering in the kind of economic no-deal calamity - a devastating recession that would see the income of the UK slashed by a tenth - that was painted on Wednesday by the governor of the Bank of England.

Which is a critique Labour will have to answer.

But in understanding the true import of what she said, Labour is arguably a sideshow.

The prime minister arrives at the G20 summit in Argentina. Credit: AP

In couching her attack on Labour in that way she - presumably inadvertently - also accused her estranged allies, Northern Ireland's DUP, and her own Brexiter MPs of the same crime, because they too hate the backstop that is designed to keep open the border on the island of Ireland (and is seen by critics as driving a wedge between GB and Northern Ireland, and sacrificing the whole UK’s right of self determination).

By advancing the argument that there is no deal without the backstop, she is telling the DUP and her Brexiters that there is no Plan B - that if they vote down her deal on 11 December, it's off to no-deal hell in a handcart of their own design.

But, rightly or not, they do not believe the choice is her backstopped deal or no deal.

Which is why they will reject her plan.

And what is potentially lethal for her is that they will on Friday feel more obliged to reject and oust her pronto, if as expected they throw out her deal - because how could they support a PM so fatalistic and negative about finding a negotiated backstop-free Brexit?

Although she keeps saying the "meaningful" vote on her deal is all about the nation, and nothing about her own future, that is not sustainable for as long as she argues that her deal is the only deal.

If she truly means what she says, that she has no plan B, she will be gone as PM within hours of losing the vote - to be replaced by someone whose heart is in finding another route to avoid no-deal mayhem.