The key Cabinet Committee on Brexit is the European Union Exit and Trade (Strategy and Negotiations) sub-Committee.  It has eleven members. Four of them backed Brexit: Boris Johnson, David Davis, Liam Fox and Michael Gove.  Seven did not: David Lidington, Philip Hammond, Amber Rudd, Greg Clark, Gavin Williamson, Karen Bradley and Theresa May herself.

Williamson has taken to lining up with the original Brexit-backers in the committee.  Bradley was added to it in February.  The reason given was that Northern Ireland’s interest needed to be represented on the committee.  This was a good point.  But Bradley’s presence on it was essential to the Prime Minister for another reason.  With Williamson going over to the original Brexiteers, the committee was divided five-five.  Bradley is nothing if not a May loyalist – she was a junior Home Office Minister under May until the latter, as Prime Minister, promoted her to the Cabinet as Culture Secretary.

Today’s Sunday Times reports that in a meeting attended by Olly Robbins, the Prime Minister’s chief Brexit adviser, officials predicted that were the Government’s position on the Customs Union to change, Johnson and Fox would resign, but Davis and Gove would not.

If this account is correct, and the calculation of those officials is that the Government could withstand those two resignations, they should think again.  As we wrote yesterday, May risks a leadership challenge if she abandons her position on the Customs Union.  The resignation of even one of the senior Brexiteers could well spark one.  The Foreign Secretary may not be the political force he was before the referendum, but he has two important Tory institutions onside: the Daily Telegraph and the Spectator.  What they said and published in such circumstances would be important.  The International Trade Secretary has been scrupulously loyal to the Prime Minister since his appointment – keeping out of the papers over Brexit negotiation differences and getting on with his job.  He is popular with the grassroots, coming in fourth in our last Cabinet League Table.  A Fox resignation could be even more damaging to May, in terms of the Party’s internal dispositions, than a Johnson one.

Furthermore, this site is not at all sure that those officials are right about the Brexit Secretary.  Resignation is not exactly anathema to him: remember the strange by-election he called over civil liberties.

Calculations are complicated by whether or not the Prime Minister would win any ensuing vote of confidence.  What would the Environment Secretary’s band of supporters in the Commons do?  We can be sure that he would be loyal if he stayed in Cabinet.  But we cannot be so certain of his backers – or of the large number of Conservative MPs, probably a majority, who believe that May cannot lead them into the next election.

As for Gove himself, he has been quiet in Cabinet and committee recently outside his brief, this site is told.  It is conceivable that in such circumstances he might argue that while he remains opposed to Customs Union membership, the Government cannot ride roughshod over the will of Parliament.  This would leave him well placed as a potential “unity candidate” in the event of the Prime Minister losing a leadership ballot.

Williamson would presumably not resign either.  But he is the last man not to have a sense of what the grassroots are thinking.  They will have the final word in any leadership election.  And, according to this site’s survey, Britain leaving the customs union, and being able to negotiate and sign its own trade deals, is their top negotiating priority.

“Jesus, Tom, I was just speculating about a hypothesis. I know I don’t know nothing,” the Police Chief says to a gangster in Miller’s Crossing.  We apologise for following in his footsteps.  But if senior civil servants can do it, then so can this site.  And so too will everyone else.

It is unlikely that the Cabinet Committee will turn turtle on the Customs Union before Commons votes on pro-customs union amendments on the EU Withdrawal Bill.  The situation is further complicated by the possibility that no amendment can be tabled that would compel the Government to join a customs union.  None the less, the position of those Cabinet Committee members is a crucial part of this chapter of the Brexit story as it lumbers towards its climax.