THERESA May risks losing control over European negotiations if MPs secure a vote to trigger Brexit talks, UK Government lawyers have insisted on the opening day of a landmark hearing at the Supreme Court.

In what is considered one of the most important legal cases in a generation, the president of the Supreme Court pre-empted proceedings by hitting out at "threats of serious violence and unpleasant abuse" received by figures involved, warning that it risked undermining the rule of law.

There were also scuffles between pro and anti-Brexit campaigners outside the court where all eleven judges will hear a case together for the first time in its history.

Read more: Theresa May faces Tory revolt over Brexit plan secrecy

Within the chamber, Attorney General Jeremy Wright said that the power ministers want to use to begin Brexit talks - the so-called royal prerogative - was an essential mechanism to "maintain control over strategy, policy and operational matters in conducting our... international relationships".

He stressed that this case was not about standing up for the rights of Parliament.

"I say Parliament can stand up for itself," he said.

"When it comes to leaving the European Union, Parliament has had full capacity and multiple opportunities to restrict the executive's ordinary ability to begin the (exit) process and it has not chosen to do so

In a written submission, the UK Government also appeared to warn that if the original High Court ruling - to hand MPs a vote to trigger article 50 of the Lisbon treaty to begin the formal process of leaving the EU - was not overturned Parliament would effectively be able to "micromanage" the talks.

Read more: Theresa May faces Tory revolt over Brexit plan secrecy

Later James Eadie QC, also for the government, argued that MPs were fully aware that they were backing the government’s right to start EU exit talks when they voted for the terms of the EU referendum.

Critics reject that argument claiming that the vote was non-binding.

Downing Street said that Mrs May was confident the government would would win the case which came as experts warned that the Supreme Court would unanimously reject the Government’s argument.

Professors from the London School of Economics (LSE) said it was “highly likely” the Government appeal would fail.

As the court heard evidence, the Prime Minister held a phonecall with her Croatian counterpart, in which she suggested that ministers, not parliament, would begin talks.

In an escalation of tensions, Downing Street also accused opposition parties of not backing "team UK".

Both Labour and the Liberal Democrats have indicated they would seek to amend any Brexit motion that came before MPs as a result of the original High Court ruling.

Other amendments could require the Government to publish a white paper on its negotiating goals or hold a second referendum on the Brexit roadmap.

Downing Street said Mrs May was respecting the referendum result "while others are seeming to make clear they want to frustrate the will of the British people by slowing down the process of leaving and trying to tie the Government’s hand in the negotiation".

Read more: Theresa May faces Tory revolt over Brexit plan secrecy

Within hours of that statement, it emerged that the Prime Minister may face a revolt by up to 40 of her own MPs over her desire to keep her Brexit plans secret.

Former Tory minister Anna Soubry predicted that as many as 40 Conservative MPs may decide to vote for a Labour motion designed to force ministers to set a "basic" Brexit aim before Parliament.

A ruling on the unprecedented Supreme Court appeal, which was launched after investment manager and philanthropist Gina Miller won a High Court case to get Parliament to vote on whether the UK can start the process of leaving the EU, is expected in the New Year.

The Scottish Government has also argued that MSPs should also be given a vote on the process of leaving the EU.

In a separate development, Home Secretary Amber Rudd has said that three million EU nationals would need identification designed to show that they came to the UK before Brexit.

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