Opposing groups of campaigners gathered outside the UK Supreme Court in London on Monday as judges started hearing the government's appeal against a ruling that Parliament must hold a vote before Britain's European Union exit negotiations can begin.

Prime Minister Theresa May plans to trigger two years of divorce talks before the end of March by invoking Article 50 of the EU's key treaty, using centuries-old government powers known as royal prerogative.

Those powers - traditionally held by the monarch but now used by politicians - allow the government to join or leave international treaties without consulting lawmakers.

Financial entrepreneur Gina Miller and hairdresser Deir Dos Santos went to court to argue that leaving the EU will remove some of their rights, including free movement within the 28-nation bloc, and that shouldn't be done without Parliament's approval.

Last month, three High Court judges agreed - but the government says they have misinterpreted the law.

The case has raised a constitutional quandary and inflamed the country's heated debate about Brexit.

November's ruling infuriated pro-Brexit campaigners, who saw the lawsuit as an attempt to block or delay Britain's EU exit.

Miller says she has received abuse and death threats.

She arrived at court Monday with her lawyers, greeted by cheers from pro-EU campaigners dressed as judges atop an open-topped double-decker bus.

A banner on the side read "In democracy, Leave hypocrisy."

"Nigel, where are you?" they sang mockingly, in reference to former UK Independence Party leader Nigel Farage, a prominent voice in the leave campaign.

He had promised to lead a march on the Supreme Court to demand judges respect the will of the majority.

It was cancelled last week after organisers said there was a risk it could be hijacked by far-right extremists.

Two anti-EU protesters held placards, one calling the case an "establishment stitch-up."

Many legal experts say the government will likely lose its appeal and be forced to give Parliament a vote.

London - 5 December 2016

1. Exterior of UK Supreme Court

2. Close up of European Union flag

3. Police entering Supreme Court

4. Wide of pro-Remain protesters from Britain for Europe singing as they arrive in open-topped London bus UPSOUND (English) "Nigel, where are you?"

5. Various of protesters outside court building, holding EU and UK flags

6. SOUNDBITE (English) David Gullant, Protester from Surrey branch of Britain for Europe:

"I am a British citizen, but I want to make sure that the UK due process is followed. So this is not about Brexit pros and cons, it's about making sure that if you have an Act of Parliament, only Parliament can change that Act of Parliament. It is not up to the prime minister to overturn it, it has got to go through due process."

7. Pro-Brexit protester Julia Waller

8. SOUNDBITE (English) Julia Waller, pro Brexit protester

"Well, I hope that the government, I hope Theresa May's hand, is strengthened. We've got to give her some credit - she can't expose her hand to Europe. Europe doesn't have our best interests at heart anyway, and I think we want to be free, and when people voted they didn't just vote for a soft Brexit or a grey Brexit, those words didn't exist then. We just voted for Brexit. We want to get out - end of (discussion)."

9. Pan from pro-Europe protesters to Supreme Court

As UK's Prime Minister Theresa May wants to start Britain's divorce from the European Union (EU), eleven judges may stand in her way.

On Monday, May's government will ask the justices of the Supreme Court to overturn a ruling that Parliament must hold a vote before Britain's exit negotiations can begin, a case that has raised a constitutional quandary and inflamed the country's heated debate about Brexit.

May plans to trigger two years of divorce talks before the end of March 2017 by invoking Article 50 of the EU's key treaty, using centuries-old government powers known as royal prerogative.

The powers - traditionally held by the monarch but now used by politicians - enable decisions about joining or leaving international treaties to be made without a vote of Parliament.

A hairdresser and a financial entrepreneur, Deir Dos Santos and Gina Miller, went to court to argue that leaving the EU will remove some of their rights, including free movement within the bloc, and that shouldn't be done without Parliament's approval.

Last month, three High Court judges agreed, but the government says they have misinterpreted the law.

Government lawyers led by Attorney General Jeremy Wright will argue this week that the British people have spoken by voting in a June 23 referendum to leave the EU.

In written arguments published before Monday's hearing, government lawyers say the use of royal prerogative to start the talks is "constitutionally appropriate and lawful."

Many legal experts say the government will likely lose its appeal and be forced to give Parliament a vote, but the government was left with little choice than to proceed with the case anyway.

"It's politically problematic, I think, to be seen to not pursue all legal avenues to obstruct this attempt to, in the eyes of some critics, derail the Brexit process," says Jeff King, Professor of Law, University College London.

In a reflection of the constitutional importance of the case - which hinges on the balance of power between Parliament and the executive - all 11 Supreme Court judges will hear the appeal, the first time the full court has sat since it was founded in 2009.

The case is scheduled to last four days, with a ruling likely in January.

Complicating the picture are new participants including the Scottish government, which argues the Edinburgh-based Scottish Parliament should get a vote, too.

Britons voted by 52 to 48 percent on June 23 to leave the EU, but voters in Scotland strongly backed staying in, and the Scottish government says they should not be dragged out of the EU against their will.

London - 1 December 2016

1. Exterior of UK Supreme Court building, traffic on street

2. Close of symbol reading (English): "The Supreme Court"

3. Various exteriors of Supreme Court building

4. Various of Jeff King, Professor of Law, University College London, looking at book

5. SOUNDBITE (English) Jeff King, Professor of Law, University College London:

"Well, I think that there are two reasons probably (why the government appealed the High Court ruling that Parliament must hold a vote before negotiations of Britain's exit from the European Union can begin). The first is that it was very confident that it would win at the beginning, and I think it's reluctant to move from that position of confidence. And secondly, it's politically problematic, I think, to be seen to not pursue all legal avenues to obstruct this attempt to, in the eyes of some critics, derail the Brexit process."

6. Cutaway of King

7. SOUNDBITE (English) Jeff King, Professor of Law, University College London:

"The reaction in some of the media (to the government's loss in the High Court), in particular in the Daily Mail and the Daily Express was, I would say, outrageous. It has been common to criticise judges in the past and I think criticism of judges is perfectly acceptable - they are public officials after all, but this type of language, 'Enemies of the people' (Daily Mail headline the day after the ruling) reminded me of the kinds of things we saw in Nazi Germany."

8. Cutaway of King

9. SOUNDBITE (English) Jeff King, Professor of Law, University College London:

"This is quintessentially a role for judges to play. It's an unclear legal position. The devolved governments don't agree, many members of parliament don't agree. There needs to be an authoritative ruling on what the role of these statutes is in the Brexit process, and that can only be given by a court."

10. Cutaway of King

11. SOUNDBITE (English) Jeff King, Professor of Law, University College London:

"I think that a government loss at the Supreme Court would not derail the Brexit process, but I also think it would be more than a mere speed bump because having to bring forward legislation to give notice would mean that there would be a participation of a much broader range of voices, both in Parliament and in the devolved legislatures and among the devolved governments. And when these voices are heard there is a political obligation of sorts to respond to these voices, to take them into account, to not proceed in a way that ignores them altogether, and I think that will make a difference to the outcome of the Brexit process, but I don't think it will stop it."

12. Cutaway of King

13. Pan of books

14. Various exteriors of Houses of Parliament

Small groups of protesters held rival demonstrations on Monday as judges inside the Supreme Court in London were hearing arguments as to whether the government had the right to leave Europe without parliamentary approval.

Britain's Supreme Court began hearing a landmark case on Monday that will decide who has the power to trigger the UK's exit from the European Union - the government or Parliament.

The legal battle has major constitutional implications for the balance of power between the legislature and the executive, and has inflamed Britain's already raw wound over how and whether to leave the EU.

Prime Minister Theresa May plans to trigger Article 50 of the EU's key treaty by the end of March, using centuries-old government powers known as royal prerogative.

The powers - traditionally held by the monarch but now used by politicians - enable decisions about joining or leaving international treaties to be made without a parliamentary vote.

London - 5 December 2016

1. Pro-Europe demonstration in front of Supreme Court

2. Tilt down of sign reading (English): "Stop Brexit fight racism and the scapegoating of immigrants. Defend freedom of movement."

3. Various of pro-Europe protesters chanting, holding banners

4. Pan from police to protesters in front of Supreme Court

5. Rival protest groups in front of Supreme Court, police officers at scene

6. Pro-Europe protesters shouting (English): "Brexit is racist, stop Brexit now!"

7. Smart phone screen showing protesters

8. Rival protesters discussing

9. Pro-Brexit protesters, woman waving Union flag

10. Man being led away by police

11. Policewoman

12. Supreme Court and protesters

LEADIN:

US President Donald Trump will pay a state visit to Britain this month as a guest of Queen Elizabeth II.

It will be the latest chapter in the president's relationship with the UK.

STORYLINE:

An oath of office and a promise to the people of the United States to "Make America Great Again".

Donald Trump became the 45th President of the United States, January 2017.

Only a week into his administration, on January 27, Prime Minister Theresa May was the first foreign leader to visit Trump.

A signature welcome, May and Trump got straight to business, holding a joint news conference in the Oval Office in Washington.

Both spoke of mutual cooperation between the two countries and agreed to "lay the groundwork for a UK-US trade agreement."

"I'm convinced that a trade deal between the US and the UK is in the national interest of both countries, and will cement the crucial relationship that exists between us, particularly as the UK leaves the European Union and reaches out to the world," said May.

"I can often tell how I get along with someone very early, and I think we're going to have a fantastic relationship," confirmed Trump.

Hand in hand, the UK-US relations were solidified.

Hours before May's arrival, Trump signed an executive order blocking entry to the UK for citizens from some predominantly Muslim countries.

The order suspended all travel to the US for citizens of Iran, Iraq, Sudan, Somalia, Syria, Yemen.

This erupted worldwide protests and ignited criticism of May's visit to the US.

April 2018 - it was announced that Trump would make a "working" visit to the UK on July 13th.

Taking the form of a giant "Trump Baby", preparations were underway ahead of his arrival.

Protesters organised an unflattering blimp for the president's visit.

July 12, Trump and his wife and first Lady Melania arrived at Stansted.

To greet them that evening, May and her husband Phillip May stood side-by-side at Blenheim palace's grand entrance.

That evening they enjoyed a lavish dinner with guests and owners Jamie Blandford and his wife Edla Griffiths.

While Melania Trump tried her hand at the centuries-old game of bowls while visiting the Royal Hospital Chelsea in London, Trump visited May's country residence, which is 40 miles (65 kilometres) from London.

May welcomed the president to Chequers in Buckinghamshire July 13.

The meeting was expected to be unusually tense after The Sun newspaper published an interview with Trump on Thursday night (July 12).

Trump was quoted as saying he didn't agree with her Brexit plan and backed Boris Johnson to be the next British Prime Minister.

But in front of the cameras, he had nothing but praise for May.

"This incredible woman right here is doing a fantastic job, a great job, and, I mean that. And I must say that I have gotten to know Theresa May much better over the last two days than I've known her over the last year and a half. I mean we've spent more time in the last two days. Yesterday I had breakfast, lunch and dinner with her, then I said 'What are we doing tomorrow?' which is today, 'Oh you're having breakfast and lunch with Theresa May.'"

"The only thing I ask of Theresa is that we make sure we can trade that we don't have any restrictions because we want to trade with the UK and the UK wants to trade with us."

That afternoon, Britain's Queen Elizabeth II welcomed Trump and First Lady Melania Trump to Windsor Castle.

A military band honoured Trump with a royal salute before playing the US national anthem.

The Queen and Trump then inspected the guard of honour before entering the castle where they were scheduled to spend about 30 minutes getting acquainted over a cup of tea.

The palace confirmed plans that Trump will make a state visit to the UK, June 3 2019.

Some of the traditional trappings of an official state visit are likely being scaled back.

Typically one of the highlights is a carriage ride procession that brings the visiting dignitary to the Buckingham Palace grounds escorted by a large number of mounted soldiers from the Household Cavalry as gun salutes are made from nearby Green Park and the Tower of London.

Officials have not said whether that will happen this time, and it may be truncated or eliminated in part due to concerns that a slow-moving procession of horse-drawn carriages could prove an irresistible target for protesters.

The president and first lady are also not going to stay at Buckingham Palace, where state visitors usually lodge, apparently because of renovations that are underway at the 775 room official residence of the Queen.

They are expected to stay at Winfield House, the spacious home of the U.S. ambassador, which has a private garden nearly as spacious as the palace grounds.

The Trumps and their grown children are expected to meet the younger generation of royals, including Prince William, a future king, and his wife Kate, the Duchess of Cambridge.

Prince Harry is also set to meet the Trumps, but his wife Meghan, the Duchess of Sussex, is expected to be at home with their son Archie.

UK Prime Minister Theresa May extended the invitation for a state visit more than two years ago, but the trip has been deferred amid concerns about the president's reception and Britain's extended crisis over Brexit.

POOL

Washington DC, US - 20 January 2017

1. Donald Trump taking oath of office AUDIO (English) Chief Justice John Roberts, off camera: "So help me, God" UPSOUND (English) Trump: "So help me, God"

2. Trump shaking hands with Justice Roberts and hugging family

3. Fireworks over the Lincoln Memorial on Inauguration night ++NIGHT SHOT++

POOL

Joint Base Andrews, Maryland, US - 26 January 2017

++NIGHT SHOTS++

4. British Prime Minister Theresa May walking down steps from plane on visit to US

5. Car driving away

ASSOCIATED PRESS

Washington DC, US - 27 January 2017

6. May's car arriving, US President Donald Trump walking to car, greeting May, May and Trump entering White House

7. May and Trump walking towards podium, holding a joint presser

8. SOUNDBITE (English) Theresa May, British Prime Minister:

"We are discussing how we can establish trade negotiation agreements, take forward immediate high-level talks, lay the groundwork for a UK-US trade agreement, and identify the practical steps we can take now in order to enable companies in both countries to trade and do business with one another more easily. And I'm convinced that a trade deal between the US and the UK is in the national interest of both countries, and will cement the crucial relationship that exists between us, particularly as the UK leaves the European Union and reaches out to the world."

9. SOUNDBITE (English) US President Donald Trump:

"I can often tell how I get along with someone very early, and I believe we're going to have a fantastic relationship."

10. Tracking shot of May and Trump walking outside White House, holding hands for a few seconds

ASSOCIATED PRESS

London, UK - 30 January 2017

++NIGHT SHOTS++

11. Close of sign that reads (English) "Shameless May, Fascist Tyrant"

12. Close of sign that reads (English) "No to racism, no to Trump"

13. Protest

ASSOCIATED PRESS

London, UK -  7 November 2018

14. Various of giant blimp balloon called "Trump Baby"

UK POOL

Stansted, UK - 12 July 2018

15. Trump and First Lady Melania Trump exiting plane, greeting others

UK POOL

Blenheim Palace, Oxfordshire, UK - 12 July 2018

16. US President Donald Trump and First Lady Melania Trump arriving by car at Blenheim Palace, British Prime Minister Theresa May and husband Philip May waiting to greet them   

17. Trump and wife Melania shaking hands with May and husband Philip

18. Trump, Melania, May and Philip walking towards the palace

19. Trump, Melania, May and Philip clapping for military parade and band

20. Trump, Melania, May and Philip and owner of Blenheim Palace Jamie Blandford and wife Edla Griffiths walking into the palace

UK POOL

London, UK - 12 July 2018

21. Security helicopter leaving and flying over anti-Trump protesters ++MUTE++

ASSOCIATED PRESS - AP CLIENTS ONLY

London, UK - 13 July 2018

22. Various of anti-Trump protesters walking on Regent Street towards Piccadilly Circus

23. Margo Steeden, protester:

"He is disrupting politics worldwide. I don't understand why the American people haven't actually removed him."

24. Tilt down on protest crowd at Trafalgar Square

25. Various of "Trump Baby" outside Westminster

26. Close of back of jacket reading: (English) "Trump Babysitter"

27. SOUNDBITE (English) Leo Murray, Trump Blimp organiser:

"We thought it would be funny, and it is funny. People are finding it hilarious."

UK POOL

London, UK - 13 July 2018

28. Various aerials of Trump blimp flying during protest ++MUTE++

UK POOL

London, UK - 13 July 2018

29. Melania Trump playing bowls at the Royal Hospital Chelsea

UK POOL

Chequers, UK - 13 July 2018

30. Trump and May posing for a photo outside the building

31. Various of Trump and May holding hands, walking to news conference

32. SOUNDBITE (English) Donald Trump, US President: ++CAMERA ANGLE CHANGES DURING BITE++

"This incredible woman right here, is doing a fantastic job, a great job, and, I mean that. And I must say that I have gotten to know Theresa May much better over the last two days than I've known her over the last year and a half. I mean we've spent more time in the last two days. Yesterday I had breakfast, lunch and dinner with her, then I said 'What are we doing tomorrow?' which is today, 'Oh you're having breakfast and lunch with Theresa May.'"

33. Wide of new conference

34. SOUNDBITE (English) Donald Trump, US President:

"The only thing I ask of Theresa is that we make sure we can trade, that we don't have any restrictions, because we want to trade with the UK and the UK wants to trade with us."

UK POOL

Windsor, UK - 13 July 2018

35. US President Donald Trump and First Lady Melania Trump arriving

36. Queen greeting Trump and Melania

37. Various of honour guard, Queen, Trump and First Lady as US national anthem is played

38. The Queen and Trump inspecting honour guard

UK Supreme Court judges were heading in for a third day of a four-day hearing as they considered whether government or Parliament has the power to lead the country out of the European Union.

Prime Minister Theresa May plans to launch EU exit talks by the end of March using ancient powers known as royal prerogative, which enable decisions about joining or leaving international treaties to be made without a parliamentary vote.

Several claimants went to court to argue that leaving the EU would remove some of their rights, including free movement within the bloc, and that such an action could not be taken without legislation in Parliament.

Last month the High Court agreed that the government cannot trigger Article 50 of the EU's key treaty, launching two years of exit negotiations, without lawmakers' support.

The government is challenging that decision at the country's top court - leaving the 11 justices to rule on the balance of power between the legislature and the executive.

CORRECTION - CLIENTS PLEASE NOTE THE MAN IN SHOT 1 IS ACTUALLY CLAIMANT CHARLIE MULLINS OF PIMLICO PLUMBERS, NOT HAIRDRESSER DEIR DOS SANTOS AS ORIGINALLY STATED

POOL - AP CLIENTS ONLY

London - 7 December 2016

1. Various of entrepreneur Charlie Mullins of Pimlico Plumbers arriving at Supreme Court. Mullins, the boss of London-based Pimlico Plumbers is one of a group of business people helping to fund the court challenge

UK Supreme Court judges were heading in for a third day of a four-day hearing as they considered whether government or Parliament has the power to lead the country out of the European Union.

Prime Minister Theresa May plans to launch EU exit talks by the end of March using ancient powers known as royal prerogative, which enable decisions about joining or leaving international treaties to be made without a parliamentary vote.

Several claimants went to court to argue that leaving the EU would remove some of their rights, including free movement within the bloc, and that such an action could not be taken without legislation in Parliament.

Last month the High Court agreed that the government cannot trigger Article 50 of the EU's key treaty, launching two years of exit negotiations, without lawmakers' support.

The government is challenging that decision at the country's top court - leaving the 11 justices to rule on the balance of power between the legislature and the executive.

POOL

London - 7 December 2016

1. Lead claimant Gina Miller and team arriving at Supreme Court

2. Lord Richard Keen QC, Advocate General for Scotland, and Jeremy Wright UK Attorney General arriving

Proceedings began on Monday at the UK's highest court as the British government attempts to overturn a ruling that Parliament must hold a vote before Britain's European Union exit negotiations can begin.

Prime Minister Theresa May plans to trigger two years of divorce talks before the end of March by invoking Article 50 of the EU's key treaty, using centuries-old government powers known as royal prerogative.

The powers - traditionally held by the monarch but now used by politicians - enable decisions about joining or leaving international treaties to be made without a parliamentary vote.

Financial entrepreneur Gina Miller and hairdresser Deir Dos Santos went to court to argue that leaving the EU will remove some of their rights, including free movement within the bloc, and that shouldn't be done without Parliament's approval.

Last month, three High Court judges agreed.

But the government says they have misinterpreted the law.

Government lawyers led by Attorney General Jeremy Wright will argue this week that the British people have spoken by voting in a June 23 referendum to leave the EU.

They say a parliamentary vote would mean getting lawmakers "to answer precisely the same question which was put by Parliament to the electorate and has been answered in the referendum."

Many legal experts say the government will likely lose its appeal and be forced to give Parliament a vote.

In a reflection of the constitutional importance of the case - which hinges on the balance of power between Parliament and the executive - all 11 Supreme Court judges will hear the appeal, the first time the full court has sat since it was founded in 2009.

The case is scheduled to last four days, with a ruling likely in January.

UK POOL

London - 5 December 2016

1. Zoom in from man waving European Union flag outside court building to flag

2. Attorney General for England and Wales Jeremy Wright arriving with his associates

3. Protest bus passing outside court, people on it chanting UPSOUND (English) "Nigel, where are you!"

4. Gina Miller, investment fund manager and philanthropist who was one of the team that won the High Court ruling, arriving with her associates, posing for photographers in front of court entrance