The government has kicked off today’s debate on the Brexit Bill with what looks, at first sign, to be a major concession: that MPs will be given a vote on the deal that Theresa May brings back.

Time to celebrate? Unfortunately not. The phrase “vote on the final deal” covers a multitude of possibilities, each of which has wildly different consequences in terms of Parliament’s ability to influence the government.

There is “accept the deal or revoke our notice to quit permanently”, the dream of the quarter of voters who consistently tell pollsters they would like the referendum result to be ignored. That is, MPs decide that the government’s deal is worse than the status quo and we decide not to leave. To be frank, this isn’t really a free choice as a majority of Conservative MPs and Labour MPs, whether through principle or fear of their voters, will never vote for such an option. This will put pressure on Labour MPs in England’s major cities and is great electoral news for the SNP and the Liberal Democrats, but in practical terms it’s not a meaningful choice, barring a significant turnaround in the mood of the House or of voters.

There is “accept the deal or send the government to try again”. Depending on how far on in the Article 50 process is, either the government could ask for extra time or revoke its notice in order to start the process again. This is the best option that could be put to MPs as far as influencing the government is concerned. Unlike undoing the referendum, it is politically tenable as far as respecting the referendum and basic democratic norms are concerned.

And thirdly is what the government is actually offering MPs, which is “accept the deal or leave on World Trade Organisation terms”. Leaving on WTO terms means a) chaos at British borders as Revenue and Customs will have to take on a far greater level of work than they have done before b) a hard border between Northern Ireland and the Republic c) severe recession thanks to the emergence of both tariff and non-tariff barriers between our trading partners. There is no deal that Theresa May could strike that would be worse than WTO terms. This is no more a choice than “a chicken sandwich or a kick in the head” is a menu.

The truth here is that all of these options remain contentious, because we haven't sought clarity from the European Court of Justice as to whether or not Article 50 is revocable, which, as I've written before, we really ought to have done before seeking to trigger Article 50. So it may be that even if May weren't offering the worst of all possible concessions, this would be the last meaningful chance for MPs to shape the deal.

And yet that’s the measure of control over the final outcome that MPs are currently on course to vote for tomorrow in the House of Commons.