Pannick moves onto jurisdiction (key issue here). Prerogative powers have been justiciable since the GCHQ case [1985] AC 374. An Order in Council made by HM on advice from the Privy Council is equally justiciable, he argues.

Pannick: the dissolution of parliament is a personal prerogative of the sovereign. That’s different from prorogation, on which the Queen must follow the advice of her ministers.

Second correction: Pannick said the dissolution of parliament WAS a personal prerogative of the sovereign until the Fixed-term Parliaments Act 2011. Apologies.

Pannick says more prerogative powers have been regarded as amenable to judicial review since the GCHQ case: the grant of pardons, mercy, refusal of passports, foreign relations/diplomatic representations — but the courts must “proceed with caution”.

Lord Burnett asks Pannick whether he says all prerogatives are justiciable. Pannick says that if a PM decides to declare war on Ruritania, no court would review such a decision — unless there is a statute or some public policy statement that restricts the PM’s discretion.

Pannick: the courts must exercise caution — sometimes extreme caution — but they can review all prerogative powers. But he accepts that personal prerogatives, eg appointment of ministers, are not covered. And there are areas where it’s inconceivable that courts will interfere.

Pannick: there should not be a separate principle of non-justiciability. In any event, executive power cannot be unlimited and the courts will enforce constitutional rules in the same way as other laws.

Pannick: court cannot say it has no jurisdiction if he has established the breach of a relevant legal principle.

Pannick deals with PM’s objections. PM says this is a matter of high policy and politics and so the court has no jurisdiction. Pannick says it may well involve those but courts still have jurisdiction. His example is the first Miller case, which involved an issue of law as well.

Pannick: PM says there are no standards by which the courts can assess the lawfulness of ministerial advice on prorogation. He replies that this is no different from any other public law case and that’s why he disagrees with Lord Doherty’s Court of Session judgment yesterday.

Pannick: I don’t accept that accountability to parliament — another of the PM’s arguments — is an answer to my claim. He says he does not accept that the NI (EF etc) Act 2019 requires parliament to sit during the prorogation that has been announced.

Pannick: PM needs to confront the breadth of powers for which he contends. If correct, why couldn’t he advise prorogation for a longer period? PM’s only response is to accept that this would be unconstitutional. PM denies that it would be unlawful. But Dicey has been superseded.

Pannick concludes his submissions after two-and-a-half hours. Sir James Eadie QC for PM begins with non-justiciability.

Eadie QC for PM: parliament specifically preserved the prorogation prerogative when it passed the Fixed-term Parliaments Act 2011, section 6 (and previously in 1707). This prerogative power has not been put on a statutory footing. It has merely been recognised by parliament.

Eadie: the question for this court is whether a specific issue is justiciable, not whether a particular power is justiciable.

Eadie: not all exercises of the prerogative are justiciable. It depends on the subject matter. Some are unsuitable for judicial intervention. Some are not justiciable. The test is not merely whether it’s the exercise of a power.

Eadie: it’s true that the courts have reviewed more prerogatives than before. That’s because these impinged on people’s rights — as in first Miller case. But power is not subject to judicial review just because it’s power. It turns on the subject-matter. Some are non-justiciable.

Eadie QC for PM is now arguing that the prorogation of parliament is inherently political and hence non-justiciable. He cites Wheeler v PM [2008] EWHC 1409 in which the court accepted that there were no judicial standards by which it could consider if there should be a referendum

Eadie QC: the rationale for non-justiciability of prorogation is there are no judicial or manageable standards to test its lawfulness and it would not be constitutionally appropriate for the courts to die so. Court adjourns until 2pm.