Even at the best of times, politics can be a place of deception and a hall of mirrors. High politics and low calculation are inseparable in the way MPs cast their votes. For some of us, that’s part of what makes politics so fascinating. But, over Brexit, the mirrors glint and deceive more than ever.

As the Commons prepares for yet another day’s voting on Brexit today, with more votes to come later this month and in March, this always needs remembering. Today’s votes are skirmishes in a campaign of positioning, not the full battle. Thus far, none of the big Commons votes have meant precisely what they may appear to mean.

Brexit: no deal still on table, says No 10, as ERG refuses to back government motion – Politics live Read more

The most prominent example illustrates this. Theresa May’s deal with the EU was massively trashed in the Commons on 15 January by 230 votes. Yet many Conservative MPs voted against it in the full knowledge that it was not the final word on the subject. Two weeks later, most of them lined up behind the so-called Brady amendment, which gives the bulk of May’s original deal a second chance.

Amid the fog of the conflict, it can be tempting to assume that more has been settled in the politics of Brexit than is the case. The reality is that most of the big options, and some small ones, are still in play. Just as May’s deal may yet survive largely intact, complete with a version of the Northern Ireland backstop, so other options that stretch from a Norway-style soft Brexit to an exit without a deal – all of which have their supporters at Westminster – cannot be ruled out.

The underlying reasons for this uncertainty are unchanged too. The European issue is huge, complex and divisive. Parliament and government are still struggling to adjust to a referendum vote they mostly do not support and which is not easy to implement. And we have a hung parliament. The combination is a recipe for instability and uncertainty.

Ever since the vote for the Brady amendment on 29 January, May has claimed that she has a “substantial and sustainable” majority for her attempt to fettle the backstop and get the deal through the Commons. Well, of course she says that. It’s in her interest. She wants to weaken the will of her rebels.

But that does not make it true. The majority for Brady was a single frame from a moving film. The movie has already moved on. May’s motion for today’s debate got into trouble with the Tory rebels yesterday precisely because it acknowledges another truth – that there is also a Westminster majority against no deal – that the rebels will not accept. Substantial majority? Pull the other one.

That is the same reason why reports of the death of the Cooper-Boles amendment have also been premature and exaggerated. That amendment, which proposed an extension to the article 50 process to prevent a no-deal Brexit, went down by 23 votes two weeks ago. One of the reasons it fell, however, is that 24 Labour MPs voted against it or abstained. Some of them did so, in part, because they didn’t want to be tarred with voting to prolong Brexit when, in fact, it may be prolonged anyway – exactly as the UK’s chief negotiator Olly Robbins was overheard predicting this week.

Whatever happens in the Commons tonight, these alternatives not only live to fight another day but may also win in the end. This week, May called on Tory MPs to hold their nerve while she continues her quest for a saleable version of the backstop. But the same advice applies with equal force to the moderates across the Commons who want to emerge with a softer Brexit deal than May has proposed. Their moment could yet come.

To say this is not to be in denial. On the contrary, it is to recognise the facts. Looking through the history of Brexit since July 2016 when she became prime minister, three truths can be discerned about May’s approach. The first is that she needs to deliver the least-worst Brexit deal for the country. The second is that she is determined to avoid no-deal. The third is that she wants Brexit to be delivered by the Conservative party and its parliamentary allies.

Her problem, all along, is that these three ducks won’t line up. That is extremely unlikely to change. The real problem is that third duck. May remains absolutely Tory-focused on Brexit. But there are not enough Tory and DUP MPs who will vote for the kind of deal she craves. The 15 January rejection, in which 118 Tory MPs voted against her deal, undoubtedly exaggerated the internal opposition. But those 118 will not all come back into line at the end of the month, or in March. Some of them will. Some of them won’t – perhaps including the DUP.

In other words, a Brexit deal will only happen with some opposition support. But how much will May need? Not even the chief whip knows. Jeremy Corbyn, who supports Brexit but who wants the Tories to own it, blurs many calculations. Yet not all of the Labour MPs who failed to support Cooper-Boles are supporters of May’s deal. Some them just don’t want to be responsible for an article 50 extension. What is more, they may get their wish, if what Robbins was overheard saying in that Brussels hotel bar on Tuesday night by ITV News’s Angus Walker were to happen.

Ever since 29 January, when the Brady amendment was carried and the Cooper-Boles amendment was lost, many have assumed that the die was cast. There is a mood of fatalism in remainer Britain that, after those votes, May is finally going to deliver a Tory-facing Brexit. Yes, that could happen. But the facts and the numbers don’t yet support that view. Facts and numbers still count for a lot, even in a hall of mirrors. But leadership counts for even more.

• Martin Kettle is a Guardian columnist