LONDON (Reuters) - Boris Johnson could recall parliament if Britain’s highest court rules he unlawfully suspended it, a government lawyer said on Tuesday, after judges heard the prime minister wanted a shutdown because it was an obstacle to his Brexit plans.

Johnson announced on Aug. 28 that he had asked Queen Elizabeth to prorogue, or suspend, parliament for five weeks from last week until Oct. 14. He said the shutdown was necessary to allow him to introduce a new legislative agenda.

Opponents said the real reason was to prevent scrutiny and challenges by parliament - where he now has no majority - to his Brexit policy, especially his promise to leave the European Union by Oct. 31 even if no divorce deal has been agreed.

They want the Supreme Court, the United Kingdom’s highest judicial body, to rule Johnson’s actions were illegal. Critics, including rebels thrown out of his Conservative Party over Brexit, say he should resign if that is its decision.

“The consequence (of his advice to the monarch being ruled unlawful) could be that he goes to the queen and seeks the recall of parliament,” Richard Keen, the government’s chief law officer in Scotland, told the court.

However, Keen was unable to rule out that Johnson might then look to suspend parliament again.

In a damning judgement last Wednesday, Scotland’s highest court said the suspension was unlawful and an “egregious” attempt to stymie parliament.

However, a week earlier the High Court of England and Wales rejected a similar case, saying the matter was political and not something judges should interfere in.

All 11 judges on the Supreme Court will now decide on a crucial question: how far Britain’s unwritten constitution limits the power of the prime minister and whether Johnson’s advice to the queen was therefore illegal.

“That this is a serious and difficult question of law is amply demonstrated by the fact that three senior judges in Scotland have reached a different conclusion from three senior judges in England and Wales,” said Brenda Hale, president of the Supreme Court.

Illustrating the deep social divisions wrought by the EU issue, angry groups of rival Brexit and pro-European supporters shouted abuse at each other outside court.

SILENCE PARLIAMENT?

Launching the legal challenge to Johnson’s decision - by a mixture of anti-Brexit campaigners and opposition lawmakers - David Pannick said there was strong evidence the prime minister wanted to silence parliament because he saw it as an obstacle.

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No premier had abused the prorogation power in this way for at least 50 years, Pannick told the court. “He ... wished to avoid what he saw as the risk that parliament would take action to frustrate or damage the policies of his government,” he said.

He said it was “remarkable” Johnson had not provided a witness statement spelling out his reasons for the prorogation and that the court could draw adverse inference from that.

Johnson has said the current session of parliament was longer than any since the English Civil war in the 17th century, and that lawmakers would have plenty of time to discuss Brexit again after an EU summit on Oct. 17-18.

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He has denied misleading the queen.

In an interview broadcast on Tuesday, Johnson declined to say whether he would recall parliament if the ruling goes against him. “I think the best thing that I can do is wait and see what the judges say,” he told the BBC.

However, Keen said the prime minister would “respond by all necessary means” to any declaration by the court that the advice Johnson gave to the queen was illegal. But asked by one judge if Johnson might seek another suspension, he said: “I’m not in a position to comment on that.”

He argued that only seven working days would be lost through the suspension, not five weeks, because parliament would be on holiday in late September as parties held annual conferences. He said the Scottish judges had a “fundamental misconception” about how parliament operated.

The government says opponents of Brexit are using the courts to try to frustrate Britain’s departure from the bloc which was approved in a 2016 referendum. But Pannick said the aim was to establish that parliament was supreme in British law and not the government.

The Supreme Court ruled against the government in a similar constitutional case in 2017 when it said ministers could not begin the formal two-year exit process without the approval of parliament. Its hearings will run until Thursday, with the verdict not expected until Friday at the earliest.

“It is important to emphasise that we are not concerned with the wider political issues which form the context for this legal issue,” Hale said. “The determination of this legal issue will not determine when and how the United Kingdom leaves the European Union.”