BREXIT: High Court in Northern Ireland dismisses first legal challenges to process

However, the case will ultimately be heard by the Supreme Court in London, which will come to the final decision, according to EU law expert Guy Lougher of Pinsent Masons, the law firm behind Out-Law.com.

"It is likely that the Northern Ireland case and the case currently in the High Court in England will be joined and sent together on the inevitable appeals to the Supreme Court, given that at their heart is the same issue: must the UK parliament approve invoking Article 50," he said.

"The stakes are enormous. If prior parliamentary approval is required before Article 50 can be triggered, there is a real risk that the necessary majority may not be forthcoming. In that scenario, Article 50 may not be triggered," he said.

Article 50 refers to Article 50 of the Treaty on European Union (TEU), which sets out the formal legal process by which a member state can leave the trading bloc. Once 'triggered', a member state has two years in which to conclude negotiations and exit the EU.

UK prime minister Theresa May has said that the government is entitled to invoke Article 50 unilaterally through use of the Royal Prerogative, rather than requiring the consent of parliament before it can do so. In two separate applications, which were heard together by the court, peace campaigner Raymond McCord and a group of politicians argued that by choosing to do so, the UK government would undermine the so-called Good Friday Agreement of 1998, which created the democratically-elected Northern Ireland Assembly and set out devolution arrangements.

The court chose to deal only with the aspects of the judicial review applications specific to Northern Irish law as part of its joined judgment, on the grounds that similar proceedings are already underway in the High Court of England and Wales. It also chose to rule on both the issue of leave to apply for judicial review, as well as the issue of appropriate relief in the event that leave to apply for judicial review was granted, as part of the same hearing due to the urgency of the applications.

In his judgment, Justice Paul Maguire said that it was necessary to distinguish between "what occurs upon the triggering of [Article 50] and what may occur thereafter".

"As the Attorney General for Northern Ireland put it, the actual notification does not in itself alter the law of the United Kingdom," he said. "Rather, it is the beginning of a process which ultimately will probably lead to changed in United Kingdom law."

"The devolved institutions [created by the Good Friday Agreement and subsequent Northern Ireland Act] do not as their raison d'etre critically focus on EU law. Their concerns and functions are much wider than this. This is not to say that the United Kingdom leaving the EU will not have effects at all but it is to say at the least it is an over-statement to suggest, as the applicants do, that a constitutional bulwark, central to the 1998 Act arrangements, would be breached by notification," he said.

Effectively, the act of notification itself would have no impact on the constitutional arrangements of Northern Ireland, or go against the terms of anything in the Good Friday Agreement or its implementing legislation, the judge said.

"The reality is, at this time, it remains to be seen what actual effect the process of change subsequent to notification will produce … While the wind of change may be about to blow the precise direction in which it will blow cannot yet be determined so there is a level of uncertainty, as is evident from discussion about, for example, how Northern Ireland's land boundary with Ireland will be affected by actual withdrawal by the United Kingdom from the EU," he said.

The judge similarly rejected arguments that the Northern Ireland Assembly would have to explicitly consent to any act of parliament triggering Article 50 by way of a Legislative Consent Motion; as well as arguments that exercise of the prerogative power was restricted by public policy or equality laws. A fifth ground for review, in which McCord argued that Article 50 could not be triggered without the consent of the people of Northern Ireland, was rejected outright by the court.