When Jeremy Hunt said on Peston on Sunday that his party faced a choice of backing Theresa May or risking seeing the UK stay in the EU, he was addressing his Cabinet colleagues Boris Johnson and Michael Gove, as much as estranged Brexiteering ultras on his backbenches.

Here is why (this is a dense and nuanced argument - but please bear with me).

The Prime Minister has clearly (and probably rightly) made the judgement that Parliament would not vote for a no-trade-deal or hard Brexit, so she has decided to concede to almost every demand made by the EU’s negotiators, so that talks on a transition agreement and trade deal can start before Christmas.

But - and this matters - the concessions she is making are anathema to Mr Johnson and Mr Gove, and a powerful constituency within her party.

As I have been saying for a fortnight, they include a Brexit divorce payment of up to £50 billion.

Health Secretary Jeremy Hunt said the party must back Mrs May. Credit: Peston On Sunday

They include a role for the European Court of Justice to adjudicate on the rights of EU migrants living here, on the occasions when the Supreme Court decides UK law is not decisive (these are likely to be rare - though for the Brexiteers it is the principle not the frequency that is hateful).

And they include a promise that there will be close regulatory alignment between Northern Ireland and the Republic of Ireland so that a hard border between the two need never be re-introduced (customs checks on goods would not be needed if product standards north and south of the border continue to be the same).

Now it is with that very last concession that the Prime Minister is taking the political risk of her life, because in that concession she is in effect saying that a trade deal for the whole of the UK will also be based on a promise of close regulatory alignment between our country and the EU, in perpetuity.

That permanent regulatory convergence between the UK and EU is her preferred route, because without it her government would collapse: Northern Ireland’s DUP MPs, which are sustaining the Tories in office, have made it crystal clear that they will not accept a separate regulatory set-up for Northern Ireland from that prevailing in the UK as a whole.

Theresa May's concessions are anathema to Boris Johnson and Michael Gove Credit: PA

But here is what I assume will be scaring the Prime Minister witless (it scares me, just as a bystander). She is signing up for close regulatory alignment between the UK and EU without ever having secured agreement for that from the Cabinet.

And for Mr Johnson, Mr Gove and most of the other more ardent Brexiteers in and out of the Cabinet, almost the whole point of leaving the EU was for the UK to “take back control” of setting rules and regulations for British businesses.

To repeat, the Prime Minister will today move very close to making a promise that would mean the UK failing to reclaim rule-making sovereignty outside the UK.

And if her own Cabinet and backbench colleagues end up vetoing that offer, even if it is accepted by Mr Juncker at Monday’s lunch, that would see the UK having no trade deal with the EU and being forced to reintroduce a peace-disrupting hard border with the Republic of Ireland.

As I said earlier, Mrs May thinks MPs and Lords would reject such a no-trade-deal Brexit as too damaging both to the UK’s prosperity and too undermining of the fragile peace in Northern Ireland.

So she is in effect playing the highest stakes game of chicken with Mr Johnson and Mr Gove - and if she loses, her Government could fall.

Or to put it another way, Jeremy Hunt might have gone further and warned his colleagues that failure to back May would see no Brexit and the probable advent of a Jeremy Corbyn administration.