LONDON — Boris Johnson's decision to suspend parliament in the run-up to Brexit will come under attack in Britain's Supreme Court on Thursday from one of his predecessors as prime minister and Conservative Party leader, John Major.

The court began hearing a third and final day of legal arguments on whether the suspension, or prorogation, was unlawful. A lawyer representing Major was due to speak against Johnson later in the morning.

The Supreme Court case stems from Johnson's decision to ask Queen Elizabeth to prorogue parliament from Sept. 10 to Oct. 14, on the grounds that he needed the time to prepare a new legislative agenda.

Johnson's opponents say the real reason why he sought the suspension was to prevent parliament from interfering with his Brexit strategy, and that he unlawfully misled the sovereign with his advice.

If Johnson loses the case, he may be compelled to recall parliament earlier than scheduled, giving additional time for legislators to scrutinize and oppose his plans to lead Britain out of the European Union, with or without a divorce deal, on Oct. 31.

Before the suspension, Johnson suffered one defeat after another in parliament, where he has no majority. Most members of the House of Commons are opposed to a so-called "no-deal Brexit" scenario, predicting that it would cause economic damage and severe disruption, including to food and medicine supply chains.

A ruling could come late on Thursday at the earliest, but is more likely to be delivered in the following days. The 11 justices have given no indication of how long they would take.

Major's lawyer, Edward Garnier, has rejected arguments from Johnson's lawyers that the suspension was a political issue, not a matter for judges. He has argued that on the contrary, judges should intervene as parliament had effectively been neutered.

"Where the effect of the prorogation is to prevent parliament from discharging its role during a time-critical period, there is no possibility of meaningful political control of that decision until after the damage has been done," Garnier wrote in a document submitted to the court before his oral statement.

Major's years in office between 1990 and 1997 were marked by bitter divisions and conflict within his party and government over Britain's relations with the EU.

The Conservatives are more divided than ever over the EU issue. Using his authority as an elder statesman, Major has said Britain should remain in the EU, and has warned that a no-deal Brexit would be disastrous for the nation.

Under Britain's complex, uncodified constitution, parliament is sovereign, although the exact scope of that sovereignty has been subject to legal debate during the Supreme Court hearing.

Lawyers representing the prime minister told the court during the two previous days of hearings that Johnson's purpose was not improper.

They also signaled that if he lost the case, he could ask the queen to recall parliament. However, they gave little clarity as to exactly how or when that would happen and what else the prime minister might do.

As well as the intervention on behalf of Major, the court was due to hear arguments on Thursday from lawyers representing various people and bodies who are not parties to the legal dispute but whose views are considered relevant and important. They include the semi-autonomous governments of Scotland, Northern Ireland and Wales. — Reuters