THE Commons meets today, only the fifth time it has held a Saturday sitting in the past 80 years; three of the previous four occasions were to deal with the outbreak of the Second World War, the Suez crisis, and the invasion of the Falklands. Whether this is a similarly critical moment for the United Kingdom depends on how MPs vote. The result is expected to be so close that no-one can predict it.

Indeed, as details of the new Withdrawal Agreement (WA) emerged on Thursday night, one breakdown of intentions suggested that a tie was the most likely result. But MPs on both sides of the Brexit divide believe that this is the moment to decide – and many of them fear it may be the last chance to avoid “no deal”.

There are complications, from amendments still seeking an extension (though the Benn Act mandated asking for one in the event that a new WA was not produced) or for a confirmatory referendum. The position of the SNP, the Liberal Democrats and, for different reasons, the DUP is straightforward opposition.

The majority of Labour MPs will also vote against (as may a few Tory ERG “Spartans”, and some of the former Tories from whom the whip was removed, though many of them are expected to return to the fold). The great uncertainty is the number of Labour MPs who might vote for the deal having, like the Tories, stood on a manifesto promising to deliver Brexit.

Even those opposed to, or sceptical about, Boris Johnson’s plans ought to concede that he has succeeded in doing what they continually asserted he could not. He reopened negotiations, as the EU insisted could not happen, and obtained the removal of the backstop for Northern Ireland. Though the new position is still a fudge, it does place any decision on withdrawal from it in Stormont’s hands, rather than the EU’s. There is more flexibility for the UK to make trade deals and removal of ECJ oversight, and “level playing field” requirements on regulation, tariffs and the like have been moved from the WA to the Political Declaration (which is not legally binding).

These are significant achievements and give the lie to claims that no meaningful negotiations were happening, or that the PM was merely stalling until a no deal exit on October 31.

But they do not, for all that, mean that this is a good deal. It is, for one thing, not a deal at all – since continued dialogue with the EU on the minutiae of a continued relationship will continue until at least the end of next year. Many MPs, with the experience of the past three years, feel that is an ambitious timetable, and that the prospect of crashing out on WTO terms remains open.

Labour has already expressed worries about the deregulatory and free-market aspects of the new WA, citing concerns about workers’ rights or the dangers new trade agreements could pose. Those concerns, however, are on the presumption that the Labour Party would not win any forthcoming general election; a UK outwith the EU under Mr Corbyn’s leadership would presumably not go down that path. The fact that some MPs may have objections to it, or even think this deal is worse than Theresa May’s, is not, however, an assurance that they are bound to vote it down.

Parliament’s primary concern has been to prevent no deal; presented with a deal, no matter how much it falls short of what they might want, MPs who maintained that they wanted to deliver Brexit, and were not secretly working to frustrate it, now have to decide whether this is their last opportunity to do so.

If the PM can convince them of that today, it will be a remarkable piece of political escapology, but even so, it will not settle everything about Brexit. One way or another, it will rumble on.