BY any reckoning, this was a devastating defeat for the UK Government. “Parliament has not been prorogued,” the Supreme Court concluded. Boris Johnson’s attempt to induce the Queen to end the parliamentary session was not only justiciable before the courts, but was categorically “unlawful, null and of no effect”.

Today, the courageous decision of Lords Carloway, Brodie and Drummond Young in the Court of Session last week stands vindicated. They got it right. Lord Doherty and the High Court of England and Wales got it wrong. But in more ways than one, the seeds of Johnson’s historic defeat were sown in Edinburgh.

The Cherry case and the Government documents it turned up shifted the argument from whether the courts should even contemplate prorogation – to the reasons why Boris Johnson sought this prorogation. Snared by its own mendacity and contradictions, the UK Government’s legal position was immeasurably weakened.

READ MORE: Time for the return of democracy and for Johnson to go

In law as in life, it’s often a good idea to listen carefully for what people are not saying. Over three days of oral argument in Middlesex Guildhall, the 11 justices of the UK Supreme Court heard from advocates representing everyone from Boris Johnson to the Scottish Government, from Gina Miller to John Major.

But what you heard – if you listened carefully enough – was a deafening silence at the heart of the UK Government’s case. Boris Johnson was represented before the Supreme Court by seasoned legal hand Sir James Eadie and Lord Keen of Elie. A former Scottish Tory chairman, Keen is the Advocate General for Scotland, owner of one small castle in Fife and one minor firearms conviction. Both are able lawyers. But their argument had a rumpled, Johnson-shaped hole at its heart: they couldn’t come clean with the court about the real reasons for prorogation. They didn’t even try.

Instead, they threw all their eggs into one basket – justiciability. The case, essentially, came down to two legal questions. Justiciability was the first. Justiciability is a lawyerly way of saying – could and should the courts take a legal view about prorogation at all? Or is the exercise of the prerogative to prorogue parliament, as the UK Government argued, a matter of “high politics” which judges have no business contemplating? Eadie and Keen went all in on this argument – and lost. And in losing this point, they were left with a threadbare case.

Because the judges were – understandably – curious about the reasons why Boris Johnson has recommended this unprecedented prorogation. What was the rational basis for it? Prime Ministers have advised monarchs on proroguing sessions of parliament for centuries. So much, so uncontroversial. But why did this Prime Minister send Jacob Rees-Mogg off to Balmoral to ask the Queen for a prorogation of this Parliament, of this length, at this sensitive – and time sensitive – moment in UK politics?

Remember, prorogation does a number of things. It ends the parliamentary session. Old bills fall. Parliamentary questions can’t be asked or answered. New legislation can’t be passed. EU Brexit deals can’t be voted on. The Supreme Court was clear the effect of prorogation was to stymie MPs’ opportunities to scrutinise Government, as October 31 rumbles towards us. But what remained foggy throughout this case were the UK Government’s reasons for doing so.

On the airwaves, Boris Johnson’s administration had been happy to answer this question. This prorogation, the PM and his ministers maintained, had nothing to do with Brexit or the ongoing negotiations with the rest of the European Union. Perish the thought. Instead, we were told, it was a chance to bring this flaccid parliamentary session to a close, and supercharge the domestic political agenda with a new Queen’s Speech.

This was an obvious fiction. But there was a simple problem with this Government spin: it didn’t cover all the bases. Say – for the sake of argument – that this prorogation really was all about polishing up this new Government’s domestic agenda. Why should this take the better part of five weeks?

If you’ve ever heard a Queen’s Speech, you’ll know they are vague, lumpy and undetailed. An outline scheme of new bills doesn’t require the better part of a month’s deliberation. Historically, prorogation has been a matter of days, maybe a week. Why should this Queen’s Speech take so much longer to pull together? Is the PM a slow study? Is there something the public should know?

Nobody inside the administration seems to have been able to come up with an honest answer to this question. There almost certainly isn’t one. The Court of Session concluded that Boris Johnson had been “motivated by the improper purpose of stymieing parliamentary scrutiny of the executive”.

The Supreme Court wasn’t prepared to go that far yesterday. It body-swerved questions of the PM’s real motives. But the bench was prepared to hold the lack of any rational reasons for this lengthy prorogation against Boris Johnson.

“It is impossible for us to conclude on the evidence which has been put before us,” Lady Hale concluded, “that there was any reason – let alone a good reason – to advise Her Majesty to prorogue Parliament for five weeks, from 9th or 12th September until 14th October.” In the absence of any good reason for it – the prorogation was unlawful, and being unlawful, null and void.

Boris Johnson was defeated by this deafening silence at the heart of the UK Government’s case. For that silence, the Government has only itself to blame. This is what comes of governing with barely concealed cynicism and gleeful bad faith. This is what comes of treating people as if their heads button up backwards. An honest Prime Minister would have nothing to fear from the courts. Yesterday, Johnson trembled.