David Cornock reports from the Supreme Court on why the Welsh Government is having a say in the Brexit case.

At the Supreme Court we are now back to the 1960s and 1970s with a reference to various pieces of legislation which formally granted independence to the Bahamas, Fiji and Barbados - which Mr Eadie says is relevant because they were "dotted around" the act which paved the way for the UK to join the then European Economic Community - the 1972 European Communities Act.

It all boils down, he says, to the circumstances in which Parliament gives or witholds permission to the government to "act on the international plane" - that's legalese for making and breaking international agreements or treaties. 

House of Commons
Parliament

The day in the House of Commons begins at 2.30pm with an hour of questions to Home Office ministers.

At 3.30pm the Green MP for Brighton Pavilion Caroline Lucas will be asking an urgent question on the "collapse" of Southern Rail services.

After that MPs will debate the Children and Social Work Bill at second reading for the rest of the day. The bill has already passed all legislative stages in the House of Lords.

Labour MP Catherine McKinnell will lead the day's adjournment debate, on support for people with terminal illness. 

House of Lords
Parliament

Image source, Getty AFP

Peers also begin at 2:30pm, with oral questions on drivers' mobile phone usage, physical education, childcare funding and the Commonwealth Heads of Government Meeting. 

Later they will be discussing...themselves - specifically, how many of them should sit in the Upper House. 

Conservative Lord Cormack has tabled this debate which will focus on ways the number of peers could be reduced. 

This debate will be briefly interrupted by an urgent question at 4:30pm on Southern rail. 

The World at One
BBC Radio 4

Former minister Anna Soubry tells The World At One that unless the government provides greater clarity on what they are seeking from Brexit negotiations, she will support a Labour attempt to compel them to do so. 

Lord Carnwath questions Mr Eadie, who will be on his feet for the rest of today's session. 

Relive this morning's session in full - the transcript of the two hour hearing is now available. Quick work by the Supreme Court team.

Here's the link, external

Mr Eadie, for the government, says Parliament carefully considered the issue of Parliament's involvement in treaty ratification, describing it as a "deliberate intervention into the field", before voting the 2010 Constitutional Reform and Governance Act into law. 

Pressed by Lady Hale on what evidence he had for this, Mr Eadie says he believes the Labour government published a white paper and there was extensive parliamentary debate. He says he will provide the necessary documentation to back this up in due course.

A few minutes later, the QC is told the green and white papers that proceeded the 2010 Act are actually able to view immediately in the evidence bundles. 

The Guardian

Columnist for The Guardian, Sarah Helm, has said during this case - one she deems as perhaps the most important constitutional case in 140 years - judges should not be attacked. 

After spending much of the morning looking at historical court judgements from the 1920s and 1970s, we have fast-forwarded to the 21st Century.

Mr Eadie raises the 2010 Constitutional Reform and Governance Act, passed during the dying days of the last Labour government, which he maintained was the first time that Parliament had explicitly considered the controls it wished to place on the government's treaty-making powers and their ratification. 

He said it was signficant because Parliament had intervened in the treaty ratification process and decided what kind of "nuanced controls" it wanted. It leaves untouched the government's power to make or negotiate treaties, he adds, as well as the process of withdrawing from treaties. 

All rise, all rise...Fortified by some light luncheon, we are back under way in the Supreme Court. Everyone is present and correct.

Lord Neuberger starts by informing everyone that one of the judges has a medical appointment tomorrow morning and it is possible that the scheduled 10:15 GMT start time might be pushed back. 

He assures government lawyer James Eadie that if that is the case and the hearing starts later, he will be able to make up the time and lunch will begin a little later.

Image source, Reuters

The UK's highest court is determining how the government can trigger Article 50 of the Lisbon Treaty - the document which sets out the constitutional basis of the European Union - in order to leave.

The government says it can do so without an act of Parliament, using executive powers. Its opponents in court say it cannot.

BBC legal correspondent Clive Coleman has written a guide to the case - Click here to read more. 

Image source, PA

The first morning of the Article 50 court case is over, but the consequences of the Supreme Court's decision are in the minds of all the parties. 

No-one can say for certain which way the case will go, but what would happen if the Government lost?

Parliamentary correspondent Mark D'Arcy looks at how the next stages of Brexit could play out. 

The World at One
BBC Radio 4

Lord Howard says he's "confident" the Supreme Court will reach "the right decision" and overturn a previous judgment requiring a parliamentary vote on triggering Article 50.

The former leader of the Conservative Party tells The World At One that the government was right to appeal that decision, and that calls from Labour - and some Conservative MPs - to reveal their negotiating stance should be rebuffed.

It is difficult to think of a court case in recent years as politically charged and controversial as the legal row over whether MPs should vote to trigger Article 50 - the process to start Brexit.

Victoria Derbyshire

The World at One
BBC Radio 4

Former Conservative leader Lord Howard tells Radio 4's World at One he expects the Supreme Court to make the "right decision", by backing the government's policy of not having a vote on Article 50 before it is triggered. 

Some people are asking ministers to disclose their position before negotiations with the EU, he adds, predicting that the "unelected, appointed" House of Lords would not stand in the way of the decision in June's referendum to leave the EU.  

The World at One
BBC Radio 4

Conservative MP Anna Soubry, who backed Remain in the referendum, says she can't understand why the government opposes MPs having a debate and vote prior to the triggering of Article 50. 

The former minister tells BBC Radio 4's World at One the "overwhelming majority" of MPs would vote for it. This is a "question of process", she adds, saying it's "important for us all to come together as a country".

She says that maybe 20 to 40 Conservative MPs could back Labour's motion calling for Theresa May to publish plans for leaving the EU in advance of Article 50 being triggered.

That motion will be debated on Wednesday.