Why Theresa May isn't ruling out another year of Brexit transition

I cannot weigh whether the reason Downing Street is not pouring cold water on the idea of an extra year of Brexit transition is simply to avoid a conflict with rest of EU tonight over dinner, and prevent another Salzburg-style debacle.

I assume that must be the reason.

Because her chief whip Julian Smith presumably has advised her that if she were to adopt the additional year of what the Brexiters see as pure vassalage - without simultaneously scrapping the backstop and Chequers - there would be (in the words of one) "the mother of all explosions".

At that instant "we would trigger a vote of no confidence in her".

She might win that vote.

But the damage would be devastating to her and her party's reputation from the formal outbreak of Tory civil war.

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PS: I understand Theresa May is prepared to agree to another year of Brexit transition (membership of EU stripped of voting rights) to 31 Dec 2021 so long as the EU abandons an "unacceptable" Northern Ireland-only backstop of customs and single-market membership.

So would Tory Brexiters buy that if her preferred backstop - of a customs territory for the whole UK with Northern Ireland in a single market with de-dramatised checks - stays in place, without end date?

That is the question on which her survival hinges. I don't know the answer.