Will the Supreme Court rule that the prorogation of Parliament was unlawful?

Is the law of the land about to put a stop to Boris Johnson's ducking and weaving round the dignified entrails of the British constitution?

Is the United Kingdom Supreme Court about to agree with its slightly junior Scottish equivalent that the prorogation of Parliament last Monday was unlawful? That would be truly sensational, unprecedented, utterly humiliating for him, and a triumph for democracy and the rule of law.

In fact it might make 2019 worth a whole chapter in any book on the British constitution written a hundred years from now. The judiciary has overruled the executive, in defence of the legislature. And the Government's somewhat desperate appeal on Friday may well confirm it. Parliament will have to reconvene, and its prorogation be annulled. The Queen, we may assume will be somewhat irritated. But she may not mind too much if she was about to sack her prime minister anyway, on the grounds that the Queen's Government cannot be conducted from a prison cell - the fate that awaits him if he ignores the law requiring him to apply for a three month extension to the Brexit deadline.

And there is a very good political reason - on top of the clear evidence that it was based on falsehoods - why the prorogation was a blunder and why Parliament needs to sit. Mr Johnson is trying out a new strategy in his attempt to agree a deal with the European Union. It involves an Irish-only backstop, with customs checks between the whole island of Ireland, north and south, and the British mainland. They would be carried out on ferries crossing the Irish Sea, or at ports of entry on the British mainland.

The beauty of it from his point of view is that this is what the EU initially agree to in its negotiations with Theresa May at the end of 2017. They would be bound to agree if asked again. She was at that point dependent on the Ulster Democratic Party for the vote of its ten Westminster MPs, to give her a majority in the House of Commons. And the DUP, through its leader Arlene Foster, vetoed it as soon as they heard of it. They were not prepared to accept any deal that treated Northern Ireland differently from the rest of the UK, while putting it in the same category as the Republic. That was, the DUP insisted, a step too far towards a united Ireland. It diminished their identity as British, and made them more "Irish". (If one detects old fashioned Protestant bigotry behind all this, one is not barking up the wrong tree entirely.)

So Mrs May negotiated an alternative that met the DUP's objections. In order that Northern Ireland would not be treated differently from the rest of the United Kingdom, the whole of the UK - England, Scotland and Wales - would have to remain inside the EU's customs union and single market indefinitely, until an alternative appeared. But then a significant section of the Conservative Party declared that this was not Brexit at all as they understood it but a betrayal of the 2016 referendum result. And they voted her deal down three times, in alliance with other parties with various other grievances. This is the mess Mr Johnson inherited.

Parliament needs to scrutinise whatever Mr Johnson is up to. Indeed it could even help him, by giving democratic legitimacy to what the DUP - who are the embodiment of fundamentalist "no surrender" Protestantism and who used to be called the Paisleyites - are about to be forced to swallow. Given a choice between that and no-deal, which would inflict grievous harm on Northern Ireland businesses, they would have little choice. Who, by and large, controls Northern Ireland businesses? The Protestants. This is a perfectly legitimate conflict of interests that the British Parliament is ideally suited to resolve. But only Parliament. He cannot solve it by himself.

Furthermore, Mr Johnson is no longer wholly dependent on the DUP's ten votes, because he has wilfully thrown away his House of Commons majority by expelling 21 Tory MPs from the party. His Parliamentary deficit is now in the 40s - ten more or less hardly matters any more.

The phrase "hoist with his own petard" must have been invented for a situation like this. It would make a good chapter heading in 2019.