The Brexiters in and around the Tory European Research Group are now telling me they are minded to vote against the Murrison/Brady amendment, which would mandate the PM to replace the backstop with some other unspecified arrangement to avert a hard border on the island of Ireland.

Why?

Well one of them told me it is because they fear it is a “bait and switch” - namely a deft con to sucker them into ultimately voting for a Brexit plan they can’t stomach.

So that seems the end of that. And proves quite how little mutual trust there is between the prime minister and much of her own party.

So there now seems little prospect of Theresa May returning to Brexit negotiations with the EU 27’s leaders in coming days armed with any empirical evidence at all about what compromise might see her plan ratified by MPs.

Any amendment would need to appease Boris Johnson and France’s President Macron. Credit: PA

Unless, that is, the prime minister can somehow persuade Tory MPs she has a credible plan to dump the backstop when she addresses her entire parliamentary party at 5pm on Monday.

There is a lot of chatter she will author her own amendment specifying how the government could no longer accept a backstop that drives a regulatory wedge between Northern Ireland and Great Britain, or represents the Hotel California of customs arrangements.

But how could such an amendment be framed - or indeed any backstop alteration - to make it embraceable by both Boris Johnson and France’s President Macron?

Truthfully I - and most MPs - remain baffled.

Which is why they are likely to break with constitutional precedent on Tuesday and wrest from the PM and the executive the power to make legislation at their own whim and at a moment determined by them, by backing the amendment of Yvette Cooper and Nick Boles.

Yvette Cooper's amendment could see Brexit delayed. Credit: PA

This would see a bill put to the house next week, which in turn would force the government to put a further motion to the Commons on 26 February, to delay Brexit - unless that is Parliament has by that juncture (and against the odds) approved a Brexit deal (sorry that is such a mouthful).

The precise length of the proposed delay to Brexit would be chosen by MPs on 26 February. And it would only happen if all EU 27 leaders agree.

For May though - in fact for any serving prime minister - the Cooper/Boles initiative is humiliation written as law.

It would be proof that on the most important voyage this country has embarked upon in fifty years, the crew have locked her in the galley and taken hold of the tiller. And although she will beg her MPs tonight not to inflict this indignity in her, too few are likely to be swayed.