ONE golden rule I’ve learned as a reporter is that it is impossible to underestimate the cynicism of politicians.

True, the press gets tarred with the same brush, but we are like newborn babes compared to our tribunes.

Just how low politicians can go was the subject of fierce exchanges at Holyrood yesterday after the UK Supreme Court handed down an important ruling of the extent of the Scottish Parliament’s powers.

Five justices, including the Scottish president Lord Reed, unanimously ruled two Bills passed by MSPs in March were flawed and so must be rewritten before they can receive royal assent and become law.

Both Bills sought to incorporate external charters into Scots law - the UN Convention on the Rights of the Child (UNCRC) and a European Charter on local self-government.

The Court said four sections of the UNCRC Bill and two in the other Bill were outside Holyrood’s legislative competence as they impinged on Westminster’s sovereign and unqualified right to make laws for Scotland, as set down in Section 28(7) of the 1998 Scotland Act that underpins devolution.

The SNP and Greens said the ruling - the result of a legal challenge by the UK Government - showed the weakness of devolution and why Scotland needs independence.

They also accused the UK Government of political shenanigans when they referred the Bills to the Supreme Court in the first place.

While the opposition accused the Scottish Government of cynically playing politics, with the UNCRC Bill in particular, in order to confect a pre-election spat with Westminster.

Who was right? Without the legal advice to both sides it’s impossible to say, but the circumstantial evidence is worth examining. The timing is key.

On March 4, Scottish Secretary Alister Jack wrote to deputy First Minister John Swinney to warn him parts of the Bills seemed to go beyond Holyrood’s powers, and asked him to amend them to keep them lawful.

Mr Swinney refused, calling the request “menacing” at Holyrood.

On March 24, after the Bills passed, Mr Jack wrote again to warn Mr Swinney the UK Government’s law officers were considering referring the Bills to the Supreme Court for a definitive ruling on their competence.

At which, the SNP immediately incorporated the issue into its Holyrood election campaign.

On March 28, Mr Swinney raised it at the SNP campaign conference.

He said: “Scotland unanimously wants to protect the rights of children - our own children - and Westminster says that we are not allowed.

“That is not just morally repugnant - it is deeply menacing. The only people who need fear this Bill are people who want to breach children’s rights. The only people who want to block this Bill are people who know they are already breaking those rights. Friends, we will not stand for it.

“If the UK Tory Government wants to target the rights of Scottish children, they had better be ready for us. We are unanimous. We are determined. And – if need be – we will see the UK Tory Government in court.”

The next day, Nicola Sturgeon put it in her speech too, contrasting Holyrood passing the legislation on the same day Mr Johnson backed nuclear weapons renewal.

“I had hoped that the Tory government might follow our lead - and ensure children’s rights would be protected and enhanced right across the UK. But not only did they refuse to follow our lead - they actually sent us a letter threatening to go to court to strike down our new law, and overturn the unanimous vote of the Scottish Parliament.

“What bothered them was that this Bill could constrain the powers of the UK Government over Scotland.

“And on the day that the Scottish Parliament was acting to protect children’s rights - what do you think Boris Johnson was doing?

“He was setting out plans to go on a nuclear weapons spending spree - to massively increase the number of nuclear warheads the UK has. “The priorities of this Tory government are all wrong. So the message is this: If you want to put children’s rights before nuclear weapons - vote SNP.”

On April 12, the UK Government confirmed it was referring the Bills to the Supreme Court. Ms Sturgeon raised it the next day in a TV debate, accusing the Tories of “failing to stand up for Scotland’s children”. Launching her manifesto two days later, she said the Tories were “even going to court to challenge a law passed unanimously [by MSPs] to protect children’s rights.”

Now, no one is saying Mr Swinney and Ms Sturgeon don’t care about children’s rights, or that they saw the UNCRC Bill from the outset as a stick with which to beat their opponents.

But when the prospect of a constitutional clash arose, they exploited it with indecent haste. It’s harder to accuse the UK Government of playing politics, as SNP MSPs did yesterday, given it warned SNP ministers in advance of a problem.

It’s also easy to see how the SNP might - and did - make hay with a row about villainous Tories and children’s rights, but not so easy to see what was ever in it for the UK Government.

As the Court’s 34-page judgment also makes clear, the six issues the UK Government raised all proved to be well-founded in law, while the Scottish Government’s case was abject.

The Scottish Government’s counsel advanced several arguments which had already been rejected by the Court in previous circumstances, including expecting the Court to take a generous view of legislation that was admitted to be outside Holyrood’s competence.

The Court was scathing about the UNCRC Bill’s “maximalist approach”, which Mr Swinney yesterday called “new territory” for Holyrood legislation. In fact, it was a mess.

The theory was that the Bill would incorporate the UNCRC “up to the absolute limits of what is possible within the boundaries of the devolution settlement”.

In practice, this meant leaving it to the courts to fathom it out all later, by going way beyond their usual role in interpreting the law.

As Lord Reed said, the UNCRC Bill appeared to have been drafted “in terms which deliberately exceed the legislative competence of the Scottish Parliament, with reliance being placed on the courts to impose corrective limitations in individual cases.”

There had been “no attempt” to draft the relevant bit of the Bill “in such a way as to provide a clear and accessible statement of the law. On the contrary, there has been a decision to draft and enact a provision whose plain meaning does not accurately represent the law, and to rely on the courts... to impose a variety of qualifications upon the provision, on a case by case basis, so as to give it a different effect which is lawful.”

In Holyrood yesterday, the Tories accused Mr Swinney of taking a “disgraceful” approach, of trying to engineer a grievance about protecting children in order to win mores votes.

He in turn blamed the “absurd” decision of the UK Government law officers to challenge the Bills.

That’s pretty rich from someone who boasted of his determination to see the UK Government in Court.

It also ignores the fact that the Court found the UK Government was right.

The Bills were flawed, as charged.

Yet Mr Swinney's apparent preference is to keep them on the statute book regardless, whatever the consequences.

Homemade trumps well made.

The main problem, in his his eyes, seems to be another government refusing to let the flaws slide, as he would.

That is a dismal stance for any legislator.

The SNP might not like the legal confines of devolution, but that’s no reason to defend bad law or complain when Holyrood is found to have made it.

As for who was the most cynical in this case, let’s just say Cui bono?