LONDON     -   Prime Minister Boris Johnson’s decision to suspend Parliament for several weeks has been ruled unlawful by Scotland’s highest civil court, setting the stage for an unusual showdown in the U.K.’s Supreme Court between the government and its opponents.

Parliament shut down earlier this week for five weeks and will remain closed despite Wednesday’s ruling. However, opposition and rebel lawmakers have already been largely successful in their plans to frustrate Mr. Johnson’s plan to quit the EU at the end of October, passing legislation that forces the government to seek an extension to the Brexit deadline if a deal isn’t agreed with the EU. With the looming prospect of an election later this year to break the Brexit standoff, a group of opposition lawmakers took their complaint to the courts. At the heart of their case was whether Queen Elizabeth was misled by the government into unlawfully suspending parliament.

On Wednesday, a panel of judges in Scotland’s highest civil court ruled in favor of a group of 78 lawmakers and others who filed a complaint to block the suspension of Parliament after the move was announced in late August.

While the suspending—or “proroguing”—of Parliament is a regular occurrence, a senior judge ruled that “it would nevertheless be unlawful if its purpose was to stymie parliamentary scrutiny of the executive.”

In the last two weeks, U.K. Prime Minister Boris Johnson has suspended Parliament, unsuccessfully called for elections, and lost his majority. WSJ’s Max Colchester explains what the recent political drama means for Brexit. Photo: Jessica Taylor/U.K. Parliament/AFP. The ruling will now head to the U.K.’s highest court, with a decision expected Tuesday. While awaiting the Supreme Court’s ruling, Parliament’s suspension until Oct. 14 stands.

In a statement, the government said the “U.K. government needs to bring forward a strong domestic legislative agenda. Proroguing Parliament is the legal and necessary way of delivering this.” Prorogation normally happens every year or so, when the government wants Parliament to start a new session so it can set out its legislative plans. The prime minster must ask the monarch to prorogue Parliament, a request which is invariably granted prompting an ancient process that involves a clerk speaking Norman French and officials in bicorn hats.

Unlike the U.S., the U.K. doesn’t have a codified constitution. It is extremely rare for a court to rule against the government on matters like prorogation that derive from the historical powers of the monarch. At the heart of the case in Scotland was whether the government had misdirected Queen Elizabeth II to suspend Parliament.

Last week, the High Court in London rejected a similar challenge by campaigners, saying the suspension was a political matter that the court couldn’t rule on. An appeal in that case is also due to be heard on Tuesday by the Supreme Court. “Boris Johnson has placed her majesty in an awkward position by providing her with advice that proved to be unlawful,” Joanna Cherry, a Scottish lawmaker who led the challenge, told the British Broadcasting Corp. Ms. Cherry called for the government to “respect this ruling.”

When Parliament was suspended in the early hours of Tuesday morning, there were protests and scuffles among some lawmakers in the debating chamber. Lawmakers tried to hold the House of Commons Speaker down in his chair—until the Speaker stands up, Parliament can‘t be suspended. Others waved signs displaying the word “Silenced.”

The complaint in the Scottish court was filed by lawmakers who largely back the U.K. remaining in the EU. While a majority of those who voted in the 2016 referendum on EU membership voted to quit the trade bloc, Scottish voters overwhelmingly opted to stay in.

 

If Parliament re-opens it could make life more difficult for Mr. Johnson, who has already endured a tough start to his tenure in Downing Street.

In the last week, opposition lawmakers have teamed up with recently expelled members of Johnson’s Conservative Party to rule out a snap election in October. They have also passed motions that seek to compel the government to disclose documents and private messages related to the suspension of Parliament and a dossier outlining the impact of a sudden “no- deal” split with the EU on the British economy.

However, British lawmakers are unlikely to sit for the whole of the coming month as they are due to attend their various political party conferences.