The High Court made a bad mistake of law in its judgment yesterday. But it was a mistake not a conspiracy and one into which the Court was led by counsel. The Supreme Court should put it right.

The mistake was to take Parliament in enacting the European Communities Act 1972 to have intended to limit the prerogative. The foundations of the mistake were the Court’s elevation of the status of the 1972 Act, by way of the new language of “constitutional statutes”, and the Court’s adoption of the claimants’ misleading analysis of the “statutory rights” to which the 1972 Act gave rise, an analysis never effectively challenged by the Government.

There has been talk in the last 24hrs about the judgment being effectively unassailable by virtue of the seniority of the judges and the force of their reasoning. This is wishful thinking. The weaknesses in the judgment are clear already and will likely become clearer still between now and the Supreme Court hearing. While it is entirely possible that the Supreme Court will double down on the High Court’s errors, if properly argued it may well fix a bad job.

A silver lining in the Miller judgment is that the Court is nothing but orthodox in its strong affirmation of parliamentary sovereignty. While the Court is wrong, to my mind, in its reasoning about what Parliament intended in 1972, the judgment is mercifully free from the sceptical asides about parliamentary sovereignty that sprout up from time to time.

But then it seems we are all true believers in parliamentary sovereignty now. For those of us whose defence of the doctrine predates June, this is a welcome development. Having said that there are reasons to fear some of this enthusiasm is strategic. And certainly it is misconceived to level charges of hypocrisy and incoherence at those who revere parliamentary sovereignty and yet also think the High Court yesterday was mistaken.

Withdrawing from a treaty may have consequences for domestic law – if Parliament has made provision to this effect, as it has in the 1972 Act – but this does not make withdrawal from the treaty itself remotely inconsistent with parliamentary sovereignty. That doctrine does not mean that every governmental power should be directly exercised by Parliament; it means rather that Parliament may make and change any law and that its laws cannot be invalidated by anyone.

The Government’s intention to trigger art. 50 by way of the royal prerogative, challenged in Miller, is entirely consistent with this rule. It is consistent also with responsible government and parliamentary democracy, for the Government is and always has been accountable to Parliament for its exercise of the prerogative.

Parliamentary sovereignty is rightly fundamental to our constitution. But the Miller judgment was not necessary to protect it and, welcome rhetoric notwithstanding, does nothing to uphold it.

Richard Ekins is Associate Professor of Law in the University of Oxford and Head of the Judicial Power Project.

Click here for further analysis of the Miller case.