Will the courts ever quash an act of parliament? The orthodox answer is, of course, ‘no’ – although there were hints to the contrary in the Jackson case of 2005 when the law lords dismissed a challenge to recent fox-hunting legislation.

Earlier this month, though, a first-instance judge decided that courts did have the power to overturn legislation if it met the traditional test for judicial review.

How was this possible? Only because the judge was sitting at the Court of Session in Edinburgh and the legislation being challenged was an act of the Scottish parliament. And Lord Emslie did not go so far as to grant the challenge: he decided that the legislation did not ‘come anywhere near the standard of "irrationality" which would be necessary’.

But Brodies, which represents four insurance companies that challenged the Scottish act, lodged an appeal to the Inner House last week. There is every chance that the case will end up before the Supreme Court in London.

That, in a sense, is where the story begins. In October 2007, the law lords delivered a judgment about pleural plaques. The case is reported under the name of Rothwell though it was known originally by the name of another claimant, Johnston.

Pleural plaques are areas of fibrous thickening of the pleural membrane which surrounds the lungs. They may be caused by negligent exposure to asbestos. But they normally have no symptoms, they produce no pain or discomfort and they are not visibly disfiguring.

Crucially, as Lord Hoffmann pointed out, pleural plaques do not cause or lead to other diseases. ‘But they signal the presence in the lungs and pleura of asbestos fibres which may independently cause life-threatening or fatal diseases’. As a result, the law lord added, ‘a diagnosis of pleural plaques may cause the patient to contemplate his future with anxiety or even suffer clinical depression’.

That, as Lord Emslie explained in the Court of Session, is because ‘the diagnosis confirms significant asbestos exposure in the past, of which [individuals] may or may not previously have been aware; it underlines the much higher risk which they now face… of contracting lung cancer, mesothelioma or asbestosis; and in some cases it may bring to mind the suffering and perhaps death of friends, colleagues and relatives’.

The law lords ruled in 2007 that claimants diagnosed with pleural plaques could not sue their employers for compensation. Neither the risk of future disease nor anxiety about the possibility of it materialising amounted to damage for the purpose of creating a cause of action.

It was a controversial decision, as I well remember. When I was asked to present an award to David Pugh, a solicitor who helped win the case for insurance companies, I was heckled by an audience of claimants’ lawyers.

And the case is no longer good law in Scotland. Last June, the Scottish parliament passed legislation – with immediate and retrospective effect – declaring that pleural plaques ‘constitute actionable harm for the purposes of an action of damages for personal injuries’.

That legislation was opposed by insurers, which now face claims for hundreds of millions – perhaps billions – of pounds from people who developed pleural plaques in Scotland. Having failed to prevent the 2009 act being passed, the insurers are now trying to overturn it.

In court, the Scottish government maintained that the insurers lacked the necessary standing to bring a challenge; the only people who stood to lose from the legislation were employers who might face actions for negligence. But that argument was roundly dismissed by Lord Emslie as ‘narrow and technical’ and ‘an affront to justice’; he found that the companies had standing both at common law and under the human rights convention.

The next question was whether ‘the validity of the 2009 act, as legislation emanating from the non-sovereign Scottish parliament, is or is not susceptible to challenge on traditional common-law grounds’.

Unlike primary Westminster legislation, subordinate legislation – made by ministers under delegated powers – is liable to judicial review. The question for Lord Emslie was whether the same rule applied to acts of the Scottish parliament. A different Scottish judge had taken the view that Scottish acts were in the same category as primary Westminster legislation.

That, said Lord Emslie, depended on whether the 2009 act contained ‘anything sufficient, whether by clear words or necessary implication, to oust the fundamental supervisory jurisdiction of the courts at common law and thus… make the [Scottish] parliament the sole judge of the rationality of its own legislation’.

In the judge’s view, it did not. If the Westminster parliament had wanted Holyrood ‘to be the first UK statutory body for two centuries or more to be wholly immune from judicial review on traditional common law grounds’, it would have said so.

However, judicial review of secondary legislation – as in England and Wales – was confined to ‘extremes of bad faith, improper motive or manifest absurdity’. This legislation came nowhere near manifest absurdity, and the insurance companies had not ‘overtly’ accused the Scottish parliament of bad faith or improper motive.

‘But if, hypothetically, a Scottish parliament were ever to legislate in a manner which could be described as a flagrant and unconstitutional abuse of power’, Lord Emslie regarded it as ‘unthinkable that the courts should have no option but to hold themselves powerless to intervene’.

And what if the Westminster parliament were to behave in such a way? Would the courts still not intervene? If this case does reach the Supreme Court, it will be fascinating to hear what the justices have to say.