The issues that will make or break Boris Johnson’s Supreme Court case

In a ruling that will have potentially seismic consequences for Boris Johnson and Brexit, the Supreme Court will decide this week whether the prime minister acted unlawfully when he suspended parliament for five weeks.

The ruling is expected on Monday or Tuesday following a three-day hearing last week, and will have major repercussions whatever decision the judges reach.

But what are the issues that will decide the historic case? The case is complex and goes to the heart of the British legal system, but there are five key questions that the judges will need to answer.

Is the issue a matter for the courts?

At the centre of the government’s case is the claim that the prime minister’s right to prorogue parliament is a prerogative power, invested in him by the monarch, and therefore not a matter for the courts.

Government lawyers argued that it was perfectly legitimate for Johnson to suspend parliament in the manner that he did, but that, even if it was not, this was a matter for parliament itself and not the judiciary. MPs had the option of passing a law to block the prorogation and failed to do so, they said. Given this, it was not for the courts to step in.

Some of the judges seemed sceptical of the suggestion that the issue is not, to use the legal term, justiciable. They asked if the government was claiming that, even if the prime minister closed parliament for as long as a year, it would still not be a matter for the courts. This is a difficult argument to make.

Lord Pannick QC, arguing on behalf of anti-Brexit campaigner Gina Miller, told the 11 judges hearing the case that the potential abuse of executive power was clearly a matter for the courts. He said that even the prime minister’s prerogative powers must have limits and one of those limits must be that the use of them should not undermine parliamentary sovereignty.

Plus, he said, if parliament is prorogued, then the courts are “the last constitutional actor” and must intervene.

Is there a limit on the prime minister’s power to prorogue parliament?

If the Supreme Court decides that the issue is justiciable (that is, a matter for the courts) then the next issue it is likely to look at are the limits – if there are any – on the prime minister’s power to prorogue parliament.

No one disputes that Johnson, like any prime minister, has this power. But the court must decide whether it can be exercised in any circumstances or whether other legal principles – such as the importance of parliament being able to fulfil its role of holding the government to account – take priority.

When deciding this, they will consider whether there are any legally invalid reasons for suspending parliament.

On this point, the government argued that there are previous examples of prime ministers closing parliament for seemingly political reasons, including several in the 20^th century.

But Lord Pannick pointed out that these were before the concept of judicial review was introduced, and therefore had not been open to challenge in the courts.

He argued that the prime minister’s power to prorogue parliament applies only until it interferes with the constitutional principle of parliamentary sovereignty.

Responding to this, government lawyers Sir James Eadie QC and Lord Keen QC said any prorogation inevitably impeded parliament’s scrutinising role and asked the court how it could possibly decide how long a suspension is reasonable and proportionate. The government’s opponents say this is exactly what the job of the courts is, and a role that they fulfil frequently.

Did Boris Johnson breach the limits on the power to prorogue parliament and therefore act unlawfully?

If the court decides that there are limits on the power to prorogue parliament, then it will need to rule on whether Johnson breached these limits in this case.

The government’s opponents argued that a five-week suspension was highly unusual and that there was no reason to have such a long break before a Queen’s Speech. They said the court should therefore infer that there was another motive behind Johnson’s decision – namely to “silence” parliament and stop it interfering with his Brexit plans.

Sir John Major, the former prime minister, supported this suggestion, arguing in a witness statement that Johnson had “ulterior motives” and that the reasons put forward by the government were “not true”.

The government insisted this was not the case. It claimed that the prorogation resulted in only seven more parliamentary days being lost because there is usually a three-week break in September to allow MPs and peers to attend the party conferences.

They said that parliament had time to pass legislation before the prorogation started and will have plenty of time after the suspension ends in which to do so before the 31 October Brexit deadline.

But government lawyers struggled to explain why a five-week prorogation was needed to allow for a Queen’s Speech, and were undermined in their argument when the court was told that parliament has not been suspended for so long before a Queen’s Speech for more than 40 years.

In truth, it may not matter what the judges think the prime minister’s motives were, if they decide that the consequence was that he undermined parliament’s power to hold the government to account.

The court was told that prorogation is much more of a barrier to parliamentary scrutiny than a normal recess, because bills before parliament are dropped, select committees do not sit and the government does not answer questions from MPs and peers.

That means that, even if Boris Johnson did not set out to obstruct parliament, that may have been the effect, and that he therefore acted unlawfully.

Even if Boris Johnson acted unlawfully in asking the Queen to prorogue parliament, was the prorogation itself unlawful?

As well as arguing that the case as a whole was not a matter for the courts, and that even if it was, that Johnson had acted entirely lawfully, the government made a third argument.

It claimed that even if it lost on its two other arguments and the court ruled that Mr Johnson’s advice to the Queen was unlawful, this did not mean that the actual prorogation of parliament was also unlawful.

This is because prorogation happens in several stages. First, the prime minister advises the monarch to suspend parliament. Then the monarch approves a Privy Council order announcing the dates when parliament will be prorogued.

The government claimed that the issuing of the prorogation order was a parliamentary matter and should therefore be seen as “forbidden territory” under article nine of the Bill of Rights – even if Mr Johnson’s advice that led to it was unlawful. This article says it is for parliament and no one else to decide how parliament governs itself.

This suggestion was hotly disputed in court. Lord Pannick said that any prorogation based on unlawful advice should itself be ruled unlawful. He argued that the prorogation order was clearly not part of parliamentary business and instead “preceded the proceedings in parliament”. It was therefore fully appropriate for the courts to declare it invalid, he said.

What should happen next?

If it declares that the prorogation was unlawful, the court may need to decide what should happen next.

During the hearing, both sides said they would be satisfied with a simple ruling on whether the prorogation was unlawful. This means that, if the judges rule against the government, they would leave the question of what happens next to the government.

It is far from clear what would happen next. Government lawyers refused to rule out Johnson suspending parliament for a second time or, depending on what the court says, refusing to recall it at all.

This means there is the potential for an explosive row – and possibly another legal battle.

Lord Pannick insisted that parliament should be recalled “urgently” next week if the prorogation is declared unlawful. If the government refuses, he said, then the speakers of the House of Commons and House of Lords could intervene to recall parliament themselves.

He asked the judges to provide some clarity by making a recommendation as to what should happen, even if they do not issue a binding order.

If Johnson is ruled to have acted unlawfully but refuses to recall parliament, the government could find itself back in court within days. This week’s ruling could be the end of the matter, or it could be just the beginning.