THE pin-striped Jacob Rees-Mogg insisted, amid all the furore over the “quasi-Remain” Chequers compromise, that one issue gave him real cause for "grave concern".

It was the fact that No 10 had been giving private briefings on Theresa May’s grand plan to Labour MPs; SNP ones were also invited in for a presentation.

"If the Government plans to get the Chequers deal through on the back of Labour Party votes, that would be the most divisive thing it could do,” declared the Somerset MP, adding: “It would be a split coming from the top, not from the members of the Conservative Party across the country."

The Downing St briefings underscore how the Prime Minister and her loyal lieutenants know that, come November, and the parliamentary vote, it will all be down to arithmetic.

While the likes of the SNP's Ian Blackford believe that having softened her Brexit stance, Mrs May will be persuaded to soften it a good deal more to fully align Britain to the customs union and the single market, her Chequers Plan, or a variant of it, could be the final destination after more talks with Brussels.

Indeed, Michel Barnier, the EU’s chief negotiator, yesterday gave rather an upbeat outlook to the months of negotiations ahead by saying he was looking forward to a “constructive conversation” and noted how “after 12 months of negotiations we have agreed on 80 per cent” and that he was determined to reach agreement on the remaining 20 per cent by November.

If the Chequers Plan or a no deal is the stark choice put before MPs later this year, then what is likely to happen?

The hardline Brexiteers obviously will not accept Mrs May's compromise but the bulk of the Tory Party could. Labour, split in half between the Corbyn Plan for a new customs union and proximity to the single market and Norway-style membership of the EEA, might equally split on Mrs May’s compromise with half abstaining and half voting for. How, one would ask, could any Labour MP vote for a no deal?

Nicola Sturgeon has said, as things stand, she could not order her SNP troops to vote for the Chequers Plan as it fell too far short of supporting the Scottish economy, so Nationalist MPs could abstain; ditto the Liberal Democrats.

So could this see Mrs May triumph in November?

Or, rather, could opposition parties vote against the Chequers Plan in the hope of defeating the PM and rather than triggering a no deal, they trigger a general election? Defeat for the Conservative leader on such a keystone issue would surely mean she would have to go the country.

But it will all depend on numbers and, of course, just how much of her grand plan Mrs May can persuade the EU27 to agree to.