Our highest court has shown its magisterial mettle, but open questions remain on withdrawal from the EU.

Enemies of the people? If that was what the headline-writers thought of three senior judges who decided in November that legislation was needed to trigger Brexit, surely they would find something even more insulting to say about the eight Supreme Court justices who agreed with the High Court in January?

Not at all. The worst the Daily Mail could throw at the Supremes was an assertion that the majority came from ‘almost identical rarefied backgrounds’ – as if to imply that the three dissenters were somehow men of the people. There was no attempt to infer their political opinions from past rulings, as we have seen in the case of Neil Gorsuch, president Trump’s nominee to a much more powerful Supreme Court.

Why the reticence? Perhaps it was the lord chancellor’s instant defence of the justices’ integrity, as reported in last week’s Gazette. Maybe it was the court’s welcome confirmation that the type of legislation needed was ‘entirely a matter for parliament’.

I doubt it. Anyone who watched the Supreme Court hearing on television could see the justices grappling with law rather than politics. And it looked as if the government would have little trouble getting its legislation through parliament with the support of the Labour front bench.

In the debate last week, some MPs found themselves torn between the will of the people and the pull of their consciences. But most felt they were required to respect the overall referendum result. How could the Supreme Court be accused of undermining democracy for giving parliament that choice?

Not that there weren’t a few rough edges left after the views of eight different justices had been shoehorned into a single text. Did they really mean to say that a prerogative power could be ‘created’ by statute? Hadn’t they misappropriated the conduit metaphor that featured so heavily in the arguments? Some of these points might have been picked up if drafts had been circulated to counsel in the usual way.

The majority found that ‘the EU treaties, EU legislation and the interpretations placed on these instruments by the [EU] Court of Justice are direct sources of UK law’. It was the European Communities Act 1972 that made it a source. Creating that source was a major constitutional change, just as removing it would be. The justices simply could not accept that this could be achieved by ministers alone.

But why not, if ministers had prerogative powers to do so? According to Lord Reed, one of the dissenters, ‘the act simply creates a scheme under which domestic law reflects the UK’s international obligations, whatever they may be’. On this view, the 1972 act is merely a conduit, a pipe running from Brussels to Dover. Bureaucrats simply pump in EU law at the Belgian end and wait until it washes up on the Channel coast – where, to quote Lord Denning, it ‘flows into the estuaries and up the rivers’. Because ministers have prerogative powers to make and unmake treaties, they can simply seal off the pipe at its source. There is no need for parliament to dig it up: it can simply rust away.

That is more logical but less plausible. Lord Reed’s dissent could have been written 100 years ago, said Dr Patrick O’Brien, LSE Fellow in Public Law. ‘It takes no account of the supremacy and unique features of EU law, finally accepted over 25 years ago by the House of Lords in Factortame (No 2).’

Ironically, it is only as parliament paves the way for the repeal of the 1972 act that we begin to understand its significance. As Pavlos Eleftheriadis of Mansfield College, Oxford has written – like O’Brien, on the UK Constitutional Law Association blog – the judgment tells us that ‘constitutional change cannot happen in the UK through practice, evolution or change of opinion’. It needs legislation.

Not that the European Union (Notification of Withdrawal) Bill doesn’t have a few problems of its own. For one thing, it permits the prime minister to notify only ‘the UK’s intention to withdraw’. Withdrawal itself is still two years off. ‘Intention to withdraw’ would have been a better phrase to have included in the bill’s short title.

The bill also leaves open the question of who takes the decision to withdraw referred to in article 50(1) of the Treaty on European Union. Implicitly, that must happen before notification under article 50(2). But is the decision one for the prime minister? Cabinet? Parliament? And under what powers?

Maybe that does not matter. Once the bill is passed and Theresa May notifies the European Council of the UK’s intention to withdraw, we may infer that the decision has been taken. It will be one that has been endorsed not only by the people but by parliament. And that is why Gina Miller’s immortality in the law reports is so richly deserved.