High Court ruling casts doubt on Brexit deadline

Downing Street indicated May would also speak to European Council president Donald Tusk and several heads of the 27 EU member states.

A spokeswoman said on Thursday that May remained determined to invoke article 50 of the EU treaty, which would formally launch Brexit negotiations, in March 2017.

”The timetable she set out at the European Council is the timetable that we are sticking to. This judgment is not going to derail that,” the spokeswoman said.

The ruling came as a blow to the government, which claimed to have a ”royal prerogative” to give effect ”to the will of the people".

The judges dismissed this argument as contrary to “fundamental constitutional principles of the sovereignty of parliament”. Only an elected assembly could take away the acquired rights of individuals - as would be the case when Britain leaves the EU.

The government immediately appealed their verdict.

The UK Supreme Court could start examining the case on 7 December, in a four-day hearing, and deliver a ruling before Christmas.

The case will likely be examined together with another appeal of a ruling, delivered by a Belfast high court last week, which said the government can launch Brexit negotiations on its own.

Way forward

UK Brexit minister David Davis said on Thursday that if the government failed to secure unique negotiating powers in the supreme court, the parliament probably had to be involved.

"We’re presuming it requires an act of parliament,” he told reporters.

That process could derail May’s timeline, even it is not clear at this stage whether the parliament would have to pass a bill, or whether both houses needed to say ”yes” or ”no” to the government’s proposal.

In the event of a vote, most MPs would probably back the start of negotiations out of respect for June’s referendum. The vote could happen quickly, even before the March deadline.

”But I don’t think this is a likely scenario,” Steve Peers, professor in the School of Law at the University of Essex told this website.

”The people that brought the case would go back to the court and say that a yes-or-no vote isn’t sufficient in this case. The government would take a huge political risk if it tried to do things this way,” Peers said, adding that this would only delay the process further.

On the other hand, a whole bill would - and should - be a complex matter.

”The parliament would take the opportunity to discuss a broad range of issues: EU-UK relations, conditions on the government for accountability in Brexit negotiations, the rights of Scotland and Northern Ireland,” Peers said.

He said there could be yet another delay to Brexit - if the supreme court was to suspend proceedings and ask the European Court of Justice (ECJ) to clarify whether a notification to leave the EU under article 50 can be revoked once it is given.

”This is relevant, because at the heart of the UK case is a dispute about the ’royal prerogative’, ie the underlying powers of the UK executive,” Peers said.

”If article 50 is revokable, the parliament doesn’t have to be involved in the triggering of article 50,” Peers said, as Westminster would have the power to revoke the government’s negotiating mandate. That would also open the way for a second referendum, on the exit terms.

The ECJ usually takes about 16 months to deliver a ruling, although it could fast-track a case such as Brexit.