There is a single important question for tomorrow's Cabinet:

Is anything the prime minister could offer the Labour Party by way of a concession that could persuade the opposition to abstain rather than vote down her Brexit plan at the fourth time it's presented to MPs (probably on Friday June 7, according to ministers).

The point is that Theresa May has given up on persuading her own rebel Brexiter MPs to come round and support her Withdrawal Agreement Bill (WAB).

In fact, those voting against it are likely to be swelled by at least two - namely Boris Johnson and Dominic Raab, who want to prove their "true" Brexiter credentials ahead of the looming election for Tory leader.

So although there are Tory MPs who naively believe she could yet amend Brexit legislation to placate Northern Ireland's DUP and her own ERG Brexiter MPs by unilaterally removing the Northern Ireland backstop, and in effect mooning the EU, I am reliably informed by her close colleagues this is NEVER going to happen.

"The prime minister is absolutely clear that the backstop cannot and will not be removed or amended by the EU," said a senior minister.

"And she won't be going back to Brussels to ask for that, ever."

So the only game in town for her is to soften the opposition of the whole of the Labour Party or a significant number of Labour MPs to her Brexit legislation, the WAB.

Theresa May's Cabinet has changed hugely since this glossy photo was taken in 2016 and it's likely attitudes toward its leader have changed too. Credit: PA

And as usual the Cabinet is split right down the middle on how far to compromise and how much to abandon traditional party loyalties.

On one side are Hammond, Gauke, Clark, Rudd and Mundell, inter alia, who would have no problem with the PM making a public pledge that if Parliament were to amend her bill so that it fully endorsed a permanent customs union, and even (possibly) a confirmatory referendum, she would not attempt to kill the legislation at the last.

I would expect the chancellor to say as much when he addresses the business lobby group the CBI tomorrow.

But there are still Brexiter members of the Cabinet - Grayling, Mordaunt, Leadsom, Fox - for whom such tolerance of such soft-Brexit or no-Brexit ideas is impossible heterodoxy.

And you never know, their patience may be tested beyond endurance, even as the PM orders in the packing cases, and they may belatedly curry favour with Brexiter MPs and members by quitting.

I am told Downing Street is braced for such unfashionably late - some would say absurdly late - virtue signalling.

But however much the PM scorns her own Brexit wing, there is a good reason why Labour will not and cannot ever support her bill or even abstain on it.

And that is because its primary aim - which you cannot fail to have missed - is to trigger a general election.

The point is that if the PM were to lose the vote on the second reading of the WAB in early June, that would accelerate her departure.

Which in turn would accelerate the likely election as Tory leader - and new PM - of either Boris Johnson (the clear favourite) or Dominic Raab.

(Tory members will never elect any candidate they perceive to have colluded in May's hated version of Brexit).

As I've said, Johnson and Raab would pledge to take the UK out of the EU without a deal, if the EU were not to bin the backstop - which in practice is an unconditional commitment to a no-deal Brexit, in that the EU will not bin the backstop.

Now although a no-deal Brexit is anathema to Labour, they do not believe Johnson or Raab could in practice deliver it.

Two of the favourites to take Tory leadership are Boris Johnson and Dominic Raab (R). Credit: PA

Although leaving the EU without a deal would warm the cockles of a majority of Tory members and maybe half of all Tory MPs, there are some Tory MPs who would rather bring down the government than collude in such an abrupt rupture.

Or to put it another way, neither Johnson or Raab can be confident of remaining PM for more than a few short minutes - since at the moment they enter 10 Downing Street, Labour would inevitably test whether they can in practice govern by triggering a no-confidence vote under the Fixed Term Parliament Act.

I imagine both have cunning plans to survive against those tricky odds.

Their conspiratorial Cabinet confreres think Raab could prorogue Parliament untill after a no-deal Brexit became a reality on October 31 and Johnson would be converted at the last to the putative merits of a confirmatory referendum.

Which would be politics as thriller or high farce.

The important point, for the opposition, is that killing the WAB would bring the kind of chaos that could see them catapulted into office, whereas supporting it would bring the kind of stability that would allow the Tory Party to regroup and rebuild.

So if you look at the UK's hundreds of years of adversarial politics, what would you expect Jeremy Corbyn and Labour to do?

There is nothing the PM can realistically offer him that could rescue her deal or her place in history.