THE insults flew thick and fast after Alex Salmond's remarkable interview on the UK Supreme Court appeared in Holyrood magazine last week.

The First Minister’s attack on the court’s role in Scottish criminal law, such as its recent quashing of Nat Fraser’s murder conviction on human rights grounds, was not a surprise. Salmond has been livid with the court and its politically awkward decisions for months.

The so-called Cadder ruling last October -- that suspects are entitled to a lawyer during a police interview -- threw the Scottish legal system into turmoil and collapsed hundreds of cases.

So Salmond sounding off was par for the course. But what was unexpected, and what took the row between the SNP and the legal establishment to a new level, was the way Salmond personalised the issue, repeatedly citing the Supreme Court’s deputy, the eminent Scottish judge Lord Hope, for “extreme” decisions which helped “vile” people.

Salmond also fulminated against the human rights lawyer Professor Tony Kelly, accusing him of trawling prison cells for clients in compensation cases, prompting Kelly to consult his own lawyers about suing Salmond for defamation.

To Salmond’s political foes it was a juvenile rant which demeaned the office of First Minister.

The Faculty of Advocates and the Law Society of Scotland also condemned him for undermining judicial independence and “the rule of law”.

Salmond refused to apologise for any of it.

But the Sunday Herald can reveal the present row may be just a warm-up act to a far bigger constitutional battle. For while MSPs were getting in a lather over Salmond’s street-fighting style, the Supreme Court was last week being asked to kill off an entire act of the Scottish Parliament.

Over three days, QCs acting for Britain’s biggest insurers argued a 2009 Act allowing people to sue for asbestos exposure should be struck down.

They claimed it was “irrational” at common law, and breached the insurers’ right to property under the European Convention on Human Rights (ECHR).

In other words, the law threatened to deprive the insurers arbitrarily of millions of pounds, as they would ultimately pay out on compensation claims lodged against employers by asbestos workers.

The insurers -- Axa, Zurich, Aviva and Royal & Sun Alliance -- had already been rebuffed twice by Scottish civil appeal courts, so were in the Supreme Court for a last roll of the dice.

The verdict is due in late August.

If the Court’s seven justices, including the Scots Lord Hope and Lord Reed, rule in favour of the insurers it means a constitutional crisis.

The Court has only ruled on one similar case -- on whether Holyrood exceeded its powers by changing sentences for traffic violations -- when it voted three-two for Holyrood’s position.

This time the stakes are far higher. Not only is a whole act of parliament involved, thousands of people exposed to asbestos are waiting on the ruling to see if they can sue negligent employers.

The power struggle between Edinburgh and London, and the emotional punch of the cases involved, would create a perfect political storm.

And if the court does set aside the act, Salmond would not be alone in his anger.

The law in question, the 2009 Damages (Asbestos-related Conditions) (Scotland) Act, had broad cross-party support at Holyrood.

It allows people to sue for damages if they have scars on their lungs known as pleural plaques. Plaques indicate exposure to asbestos but aren’t harmful in their own right -- they’re generally symptomless and don’t contribute to or mutate into asbestosis, lung cancer or mesothelioma.

In 2007, the House of Lords ruled insurers no longer had to pay damages for them, as they caused no physical harm.

The Holyrood act restored the right to sue for plaques on the ground they caused psychological harm, as people with them knew they had been exposed to asbestos and worse might follow. Justice Secretary Kenny MacAskill said it was the law he was most proud of passing.

MSPs of all parties would be horrified at devolved law-making being overturned by unelected judges, especially as acts passed by Westminster, as the national parliament, are essentially off limits to the Supreme Court.

Salmond told the Sunday Herald in an interview before the election which is published for the first time today that if the judges threw out the Holyrood act it ‘‘would indicate the Supreme Court has embarked on undermining the Scottish judicial system”.

He added: “We restored the position to what was thought to be the legal position before the Lords judgment, and that’s now been tested twice in the Court of Session. I think it would be an altogether undesirable thing for the Supreme Court to countermand the highest court in Scotland yet again. People may start to ask, ‘Is this the purpose of the Supreme Court?’”

Constitutional expert Alan Trench, author of the Devolution Matters blog, said: “If the statute were held to be irrational or unlawful, it would be a crisis no matter who was in office -- but in the present climate, one would expect the First Minister and SNP to make the most of it.”

But even if the court says this particular act is competent and ECHR-compliant, it was also asked if Holyrood laws can be challenged under common law, which could have huge consequences for future legislation.

The 1998 Scotland Act says Holyrood laws can only be challenged if they intrude on reserved issues, or breach European law or violate the ECHR.

If the Supreme Court said an act could also be reviewed on common law grounds it would open the door to a host of other challenges, such as irrationality, illegality or faulty procedure. In effect, Holyrood laws could be overturned in the same way as dodgy council decisions.

Dr Aileen McHarg, senior lecturer in public law at Glasgow University, said the insurers “are basically arguing that you should treat the Scottish Parliament like a public authority, like a local authority or a minister, and review them on the same common law grounds. That is potentially highly significant.”

She said: “It’s possible [the judges] could find that the [Damages] Act is perfectly OK, but nevertheless say that in principle acts of the Scottish Parliament are reviewable at common law.

“The Scottish parliament would want to argue it’s not just another public authority -- it’s a legislature and it should be treated more like Westminster, which is not challengable on standard judicial review grounds.

“Once you open the door to common law challenge, that door can be pushed open wider in other cases.”

The Association of British Insurers declined to comment.