Did May or Labour win in yesterday's Brexit vote?

Brexiteers are crowing "victory at last" over yesterday's overwhelming vote by MPs in favour of triggering Article 50 by the end of March.

And of course it matters that the Commons has for the first time approved Theresa May's timetable for beginning negotiations to get us out of the EU.

But this is symbolism: the vote on an opposition day motion has no binding force in law.

Which is why, as I said before the vote on Tuesday night, the prime minister's u-turn on publishing a Brexit "plan" - which MPs also approved yesterday - is a fig leaf, which she intends to honour in the letter rather than the spirit.

To repeat, if she gets her way the plan will be the least detailed and prescriptive plan in history, the equivalent of Johnson's having-and-eating cake dictum.

But here is where it would be naïve to presume that Kier Starmer, Labour's Brexit spokesman and a former top lawyer, has been comprehensively outmanoeuvred by Downing Street.

Because he knows the real Article 50 action from a constitutional viewpoint didn't happen in the Commons yesterday but is taking place 100 imperial yards away across Parliament Square at the Supreme Court.

That is where it is being decided whether formal legislation, rather than an advisory motion, is necessary before the UK can begin to withdraw from the EU.

If the Supreme Court judges rule that since legislation was needed to get us into what was at the time called the Common Market more than 40 years ago legislation is now needed to get us out, then Theresa May's agreement to publish a plan will became a very serious millstone for her.

The point is that MPs and Lords would be abdicating their duties under our constitution to pass any law, however trivial, without giving it proper prior scrutiny.

For them to pass arguably the most important economic and constitutional law in our post war history, a Brexit bill, as a rubber-stamping exercise would be to demean the authority of parliament to a degree that could be irredeemable.

So MPs will rightly want a proper debate, while signalling - of course - that they will not frustrate the revealed will of the people, so they will not stymie the triggering of Article 50.

In those circumstances, if the government and Theresa May were still to refuse to provide a detailed description of the varying costs and benefits of different versions of Brexit, it and she would be open to the legitimate charge that they do not have a clue what they are doing.

So confronting the Supreme Court is a decision that will not only determine the process for leaving the EU, but also the future balance of power between Parliament and the executive.

It is a decision that will recalibrate the delicate distribution of rights and responsibilities within the Britain constitutions for decades - and on the immediate perception of May as strong or the prisoner of events.