The British government’s plans to commence the process of leaving the EU speedily this spring were injected with uncertainty as the Supreme Court ruled that the government cannot trigger Article 50 — the EU article that sets out how a country can leave the union — without a parliamentary vote. It upheld the verdict of the High Court last year.

However, the court ruled that the government would not have to consult the devolved legislatures in Northern Ireland, Scotland and Wales.

The government, which has accepted the verdict, has said it plans to stick to the existing timetable to trigger Article 50 by the end of March.

Brexit Secretary David Davis told the House of Commons on Tuesday legislation will be introduced in a matter of days, to give the government the legal power to commence Brexit negotiations.

“This will be the most straightforward bill possible,” he told the House of Commons during a lively session on Tuesday. It is right that Parliament scrutinise and debate, he said, but it should not “thwart” the “will of the people” or disrupt the government’s timetable.

By eight to three, the justices ruled that the government could “not hold any power if it would thereby change UK laws, unless it is authorised to do so by Parliament,” Lord Neuberger, President of the Supreme Court, said on Tuesday, accepting the claimants’ argument that leaving the EU would change UK law and the rights of its residents.

The justices rejected the government arguments that the 1972 European Communities Act allows for minsters to withdraw from EU treaties without going to Parliament.

On the devolution issue the court considered the Sewel Convention that states that Westminster did not legislate on devolved issues, and ruled that while the convention played an important role, the “policing of its scope and operation is not a matter for the courts.”

Though the judgment was widely expected — and the government has insisted it will stick to its original timetable of triggering Article 50 by the end of March — it is a significant blow for the government, which has clung on to its insistence that the executive’s prerogative powers could see it through the triggering of Brexit.

In her speech last week, Prime Minister Theresa May conceded parliamentary involvement but only to give the final Brexit deal the go-ahead, well after Article 50 had been triggered.

“Only Parliament can grant rights to the British people and only Parliament can take them away. No Prime Minister, no government, can expect to be unanswerable or unchallenged, Parliament alone is sovereign,” said Gina Miller, one of the claimants, speaking outside the Supreme Court.

Labour Leader Jeremy Corbyn said that while his party would not “frustrate the process for invoking Article 50”, it would seek to amend the bill to prevent the government from turning Britain into a “bargain basement tax haven off the coast of Europe.”

Added uncertainty The Supreme Court result has added uncertainty to the government’s timetable.

While the Liberal Democrats (who hold nine seats in Parliament) have said they will vote against the triggering of Article 50 unless a second referendum on the terms of Brexit is held, the Scottish National Party (which has 54 MPs) has said it could bring as many as 50 amendments to the legislation.

Labour’s Shadow Brexit Secretary Keir Starmer said the party will be seeking amendments to ensure proper scrutiny and accountability throughout.

“The end result will be better if scrutinised than it would otherwise be,” he said. Labour holds 229 seats to the Conservatives’ 329. The government also faces the prospect of opposition — and amendments — in the House of Lords, where the government’s ability to control the timetable is more limited, and where the Conservatives do not have a majority. However, it is still possible for the government to force the legislation through the Upper House rapidly if needed.

Second referendum While the developments regarding the devolved governments will have been welcomed in UK government circles, it also adds to longer term tensions: the Scottish government has said it could push for a second referendum in the wake of a hard Brexit, and Tuesday’s verdict is likely to breathe life into the independence movements.

“It is becoming clearer by the day that Scotland’s voice is simply not being heard or listened to within the UK,” said SNP leader Nicola Sturgeon on Tuesday.

It also has to be remembered that the court case, though the most high-profile, is not the last legal challenge to the government’s Brexit plans. There are more challenges including a move to require the government to keep the UK in the European Economic Area, and even legal challenges in Dublin due to commence later this week.

The Brexit referendum and the role of parliament and government have divided society like few others: Miller, the claimant, has spoken repeatedly about the torrent of hate she has been subject to since commencing her court case. On Tuesday she called on public figures to be more outspoken in condemning such hate.

Things were quiet outside the Supreme Court as the judgment was delivered —a handful of protesters gathered in the icy conditions.

However, media outlets that supported the Leave campaign were quick to post incendiary headlines: “Yet again the elite show their contempt for Brexit voters!” screamed the headline on the Daily Mail website.

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