Theresa May's bold new plan for the Withdrawal Agreement Bill is a not quite Ramsey MacDonald: a Tory Prime Minister bending to the Labour position, but not quite.
The new customs union proposal is temporary for one Parliament only (in the legislation).
The new confirmatory referendum within the legislation is (as I understand it) a kind of indicative vote dependent on the bill going through, in that MPs voting and losing on a confirmatory referendum would be committed to passing the bill. This is done by offering a vote on the confirmatory referendum after the second reading. Surely if this was an amendment that was lost, supporters of the referendum would then vote against the bill on third reading. But this does not come with government support, but only an option, and MPs on the payroll vote would do what they wanted individually. It is not enough for those who want a second referendum locked in with a deal passed.
The third main element, of 'match UK customs to Northern Ireland' if the backstop comes, in is supposed to appeal to the Democratic Unionist Party.
The Ramsey MacDonald sway (he was a Labour Prime Minister who headed a National Government with the Conservatives and Liberals in 1931) is enough to lose her own Conservative Party support, but it is not enough to attract enough Labour MPs. It will keep those like Caroline Flint, but hasn't quite attracted Lisa Nandy - and she is exactly the person the Prime Minister needs on board. Andrew Percy is a Tory MP who has supported the government's meaningful votes so far, but won't support this. So it looks like a serious net loss. The Tories may end up with the payroll vote and little else. If you are going to do a Ramsey MacDonald, then you may as well do it.
Her point is that the Cabinet went as far as it could go to propose a temporary customs union, but to appeal to Labour it must meet the permanent customs union demand of Labour. May is losing votes before she attracts them! But surely the Cabinet passed it because all ministers knew that Theresa May could introduce the bill, lose it and we move on anyway, as members of this Cabinet and others declare for leadership anyway.
The Democratic Unionist Party has already said no to this new plan. The problem is that the backstop could come in while there is divergence going on; the backstop would require reversal of divergence. The backstop comes in if there is no trade deal with the EU, but the UK would be already free to make deals elsewhere and thus begin divergence. This just does not work: it only works if the UK stays in the Customs Union. Adding UK legislation on Great Britain to a treaty on withdrawal that does not contain that legislation won't appeal to the DUP.
The SNP won't support it, because it ignores the Single Market (at the very least), and the Liberal Democrats have declared "Bollocks to Brexit" already, and the Greens wish to stay in. Change UK are moving towards the practicality of revoke, which Vince Cable has said may have to be so if to be regretted.
So the new deal for the Withdrawal Agreement Bill is still born. Good. We face the need to revoke, and the benefit of revoking to end the nightmare.