Europe's attention will be drawn to a small corner of Westminster as the Supreme Court hands down its historic ruling on Article 50 of the Lisbon Treaty on Tuesday morning (24 January).

Theresa May had planned to circumvent parliament and trigger the mechanism to break away from Brussels without a vote from MPs. But investment fund manager and Remain voter Gina Miller successfully challenged the government at the High Court last November.

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Three judges rejected Attorney General Jeremy Wright's defence that the government had the legal authority to invoke Article 50 without consulting parliament because of so called "residual" prerogative powers from the crown.

Since parliament had a vote on the European Communities Act 1972, the legislation which enshrined the UK's membership of the precursor to the EU, there was no precedent for the government to use prerogative powers on EU-related law.

However, the government appealed the High Court's decision at the Supreme Court in December. The landmark case will come to a conclusion around 9.30 GMT after a four-day hearing and deliberations from 11 justices.

"We are not being asked to overturn the result of the EU referendum," Lord Neuberger, the UK's most senior judge, said in December. But the Supreme Court's decision could scupper May's Brexit plans.

The prime minister has promised to invoke Article 50 by the end of March. If the Supreme Court upholds the High Court decision and parliament is given a vote, the timetable could be pushed back as May faces likely opposition in the House of Lords.

The judges will also decide on whether the devolved administration of Wales, Northern Ireland and Wales should have a greater say on the Brexit process. First Minister of Scotland Nicola Sturgeon has continuously raised concerns about May's "hard Brexit plans".

Agata Gostyńska-Jakubowska, a research fellow at the Centre for European Reform think-tank, said: "If the Supreme Court rules that devolved administrations should also have a say in the Brexit process, though this looks unlikely, May might find it difficult to activate article 50 by the end of March 2017.

"She has been dismissive of the concerns of devolved governments ever since the outcome of the referendum, so they have no reason to make it any easier for her now."

Theresa May's 12-point Brexit plan

  1. Government will provide certainty and clarity to politicians and businesses.
  2. UK will 'control our own laws' by quitting the European Court of Justice.
  3. Strengthen the 'precious union' between England, Wales, Northern Ireland and Scotland.
  4. There will be no hard border between Northern Ireland and the Republic of Ireland.
  5. UK will 'control' EU immigration, while recruiting the 'brightest and the best' from around the world.
  6. Government will seek a reciprocal residency rights deal for EU and UK workers 'as soon as possible'.
  7. To protect workers' rights.
  8. Ministers will seek a 'bold' and 'comprehensive' free trade agreement with the EU.
  9. UK will seek a customs agreement so that it can broker its own trade deals with non-EU nations.
  10. Maintain European science and innovation ties in bid to keep the UK a 'world leader'.
  11. UK will continue to work with the EU to combat the threat of terrorism.
  12. Ministers will seek to avoid a 'cliff edge' and seek a smooth split from the EU.
Supreme Court Brexit European Union Theresa May