The British government's appeal against a legal ruling that it needs parliamentary approval to trigger the formal process of leaving the EU is being heard in the country's top court this week. Prime Minister Theresa May has announced that she will invoke "Article 50" of the EU's Lisbon Treaty by the end of March and begin the formal Brexit negotiations with Brussels. But London's High Court ruled last month that the government does not have the constitutional right to start the process without the backing of lawmakers.
How does the Supreme Court work and how will the case be argued?
The Supreme Court currently has 11 justices who are selected by an independent commission and must have either been a High Court judge for two years or a practising lawyer for 15 years.
The president of the court is David Neuberger, who worked at merchant bank N M Rothschild & Sons before switching to law in 1974. The vice-president is Brenda Hale, who was Britain's first female law lord. The other justices are Jonathan Mance, Brian Kerr, Anthony Clarke, Nicholas Wilson, Jonathan Sumption, Robert Reed, Robert Carnwath, Anthony Hughes and Patrick Hodge. Usually four or five justices sit on a panel considering cases. However for the first time, all 11 justices are sitting "en banc" to hear the Article 50 challenge.
A simple majority is needed for a judgement. The case will be held over four days from December 5-8. The judgement will follow at a later date, probably in mid to late January.[caption id="attachment_38567" align="aligncenter" width="800"] A grab taken from the televised live feed shows James Eadie QC, right, speaking at the Supreme court on the second day of a hearing to decide whether or not parliamentary approval is needed before the government can begin Brexit negotiations on December 6, 2016 in London. AFP[/caption]
It centres on who has the constitutional right to invoke Article 50 of the EU's 2009 Lisbon Treaty, the formal process by which Britain notifies the European Union of its intention to leave the bloc, kicking off two years of negotiations. All parties in this case agree the Article 50 process is irrevocable, so as soon as it is triggered, Britain will inevitably leave the EU at some stage. However, some EU and legal experts believe this is a misreading of Article 50 and that Britain could change its mind at some time in the future even after triggering it.
It is possible that the justices might themselves seek an answer to this question which would mean they would have to consult the European Court of Justice, something which might delay the case.
At the High Court, the claimants successfully argued only parliament could start the exit process. Their case was that rights that were incorporated into British domestic law by the 1972 European Communities Act by which Britain joined the bloc could not be taken away without parliament's approval as it is the sovereign body in Britain's unwritten constitution.
If the government loses it will have to secure some form of parliamentary approval to trigger Article 50. This could be achieved through a substantive motion, a proposal put forward for debate and a vote, which would take little time. However, the claimants say there needs to be new primary legislation that passes through both parliamentary chambers, a far more complicated process.
While it is possible legislation could be introduced and passed between the time of a final judgment late this year, and May's end-of-March 2017 deadline, it is likely to be tight and may result in the triggering being pushed back.
The 1972 European Communities bill, which set the terms of Britain's entry into the European club, involved a total of about 40 days of debate during its passage through parliament, according to the Institute for Government.
Lawmakers could also add amendments demanding additional scrutiny of the government Brexit plans which could complicate their negotiating position.
Out campaigning in Sleaford asking people to send the Government a message and get on with Brexit. pic.twitter.com/Xieq7IAAiB— Nigel Farage (@Nigel_Farage) December 5, 2016
Lawmakers in the lower house, the House of Commons, are unlikely to try to block Brexit, as it was backed in a popular vote, and a Reuters survey suggested many MPs who voted to "remain" would now approve the triggering of Article 50 in a parliamentary vote.
However, a cross-party group of lawmakers, who support a "soft Brexit" have demanded a greater say for parliament in negotiations and say they might try to pass amendments that guarantee this.
The opposition Labour Party has said it would seek amendments to ensure access to the European single market and to protect workers' rights.