If the Supreme Court cannot protect us from abuses of power, then who will?

They say it takes one to know one, so the evidence provided by Sir John Major, former Conservative prime minister, about Boris Johnson, current Conservative prime minister, about the extraordinary prorogation of parliament has at least some curiosity value.

It is yet another “unprecedented” development of so many during the Brexit saga. Indeed, Sir John could, quite easily, have been joined by all of Mr Johnson’s living predecessors in attesting to his strange and unnatural suspension of the House of Commons. If they had turned up in court Sir John, Tony Blair, Gordon Brown, David Cameron and Theresa May would have made quite a spectacle. They’d not agree on very much, but it may be fairly said that they share a low-ish opinion of the qualities of the current resident of Number 10 Downing Street.

Like the others, Sir John has been there and done that in regard to prorogation. He has been labelled a “hypocrite” because he is supposed to have himself shut the Commons down early in 1997, to avoid giving extra publicity to the “cash for questions” controversy, but it is not entirely clear that it was either his intention or the effect of his decision. In any case, the decision he made at that time was not challenged in any court, and therefore its legality, or constitutionality, was not tested. In other words, even if Sir John is indeed the most awful hypocrite ever to stalk the Supreme Court of the United Kingdom, hypocrisy is no more than a moral offence, usually dealt with in a trial by media.

As to the substance, though, Sir John’s points stand. His judgement is that the government’s decision to prorogue parliament at a crucial moment was unconstitutional and was so in its intent. That is, it was designed to deprive the Commons, in particular, of holding the executive to account over Brexit; and to prevent the Commons from legislating as it saw fit about Brexit in good time (though in fact it did succeed in doing so in the event).

If the prime ministerial power to advise the monarch in a binding way to prorogue parliament is a purely political matter, not justiciable by the courts and untrammelled by any time limits or other conditions, either under statute or convention, then any government at any time can rid itself of the inconvenience of parliamentary scrutiny for prolonged periods. That cannot be constitutional, and defies the sense of the statutes and conventions that make up the mostly unwritten British constitution as it has evolved since the 17th century. The Supreme Court cannot, in effect, sanctify and condone such a constitutional doctrine.

Constitutions, written or unwritten, inevitably evolve, but they do so through the interaction of many forces – the executive, legislature, courts, political parties, people, vested interests. They do not do so just on the whim of one prime minister in a tight corner.

The questions, though clouded in legalese and sometimes arcane procedure are in reality fairly clear. First, is the matter justiciable? If the Supreme Court has a role in defining and judging on the British constitution – and there are many examples of it and its predecessors doing so – then the answer in principle must be yes. If the Supreme Court cannot sort this out, then no one can.

Second, then, is whether the advice the prime minister offered to the Queen was contrary to the constitution, either under Scottish or English law. The lower Scottish court judged it was improper; the lower English court that it was OK and, in essence, that’s all’s fair in love and war.

In the absence of witness statements from Whitehall officials, ministers and the prime minister (let alone the Queen and her advisers), we are left with the redacted documents entered into court by the government; their public statements and activities; and various other pieces of what might be called circumstantial and “expert evidence”, such as Sir John’s. Taking a step back, it seems plain, on the balance of the evidence, that the government’s decision was in part driven by wishing to have a fresh session and a new Queen’s speech. But it was also demonstrably driven by an understandable aversion to having parliament “interfere” in the Brexit talks at a critical and sensitive point. However, parliament’s job is to “interfere”. It has an inalienable constitutional right to do so, and if it is prevented from doing so by some abused constitutional administrative device such as this, for which prorogation was never intended, then that must be irregular and unconstitutional: parliament did not vote to be suspended – no one asked it.

Third, in the light of another absurdity raised outside the court in recent days, if the prorogation is ruled unconstitutional, then does the government have the right to simply announce a second prorogation immediately after a recall of parliament? The answer to that was suggested by former Supreme Court justice Lord Sumption, in a different context, who reminds ministers that the courts are not given to allowing recalcitrant parties to play with legal loopholes. In one sense, in fact, there is no such thing as legal loophole if a court is unwilling to allow it. The courts do not mess about.

Momentous as the Supreme Court’s decision is, parliament has already ensured that no-deal Brexit has been outlawed in any case before 31 October, and some extension to Article 50 will have to be requested sooner rather than later – and there is no way that Number 10 can evade the clear purpose of the law. The Supreme Court decision will have no immediate impact on that in any event. What it does mean, though, is that the Commons will be simply able to do its job as and when it wishes. The Supreme Court is merely enforcing the Commons’ prerogatives and rights, and helping MPs to “take back control”. If MPs and peers then wish to approve a Brexit deal, cancel Brexit or replace their latest laws and go for a no-deal Brexit, or vote for a general election, then they must have the time and space to do so. They must have ultimate control over events, a veto, on behalf of their constituents. There is something very apt about such a conclusion to this nasty little business.