- Video by ITV News Political Correspondent Paul Brand
The UK's highest court has been told how the 'mother of parliaments been shut down by the father of lies', in a case judging the legality of Boris Johnson's prorogation advice to the Queen.
Lawyers arguing against the prorogation claimed it was the duty of the Supreme Court to be the "only constitutional actor left standing" when Parliament is suspended.
Aidan O'Neill QC urged the 11 justices hearing the case to "stand up for truth, stand up for reason, stand up for diversity, stand up for Parliament, stand up for democracy by dismissing this Government appeal".
He went on: "What we have with prorogation is the mother of parliaments closed down by the father of lies. Lies have consequences - but the truth will set us free.
"Rather than allow lies to triumph, this court should listen to the angels of its better nature and rule that this prorogation is an unlawful abuse of power of prorogation which has been entrusted to the Government."
But government lawyers disagreed, saying the advice to the Queen was not for any "improper purpose".
Sir James Eadie QC said decisions to prorogue Parliament "are inherently and fundamentally political in nature" and not a matter for the courts.
He added how the suggestion the prorogation was intended to "stymie" Parliament ahead of Brexit is "untenable".
He said "prorogation can exist in a whole varierty of different contexts" and added that Parliament could have taken action to prevent it being prorogued.
But lawyers arguing against the government claimed the Supreme Court did have the power to rule that Mr Johnson's decision was unlawful.
Mr O'Neill said: "Once Parliament has been prorogued, the only constitutional actor left standing is the courts."
Referring to the Government's failure to submit a witness statement or affadavit to the court, Mr O'Neill said that it could normally be assumed that the Government would not resort to "low, dishonest, dirty tricks - but I'm not sure we can assume that of this Government".
During a series of exchanges with judges on the second day of the historic hearing in London, Mr Eadie said any attempt to call Mr Johnson to give evidence in court would have been "resisted like fury" had it been made.
The Supreme Court is hearing historic appeals from two separate challenges brought in England and Scotland to the prorogation of Parliament.
Sir James told the court on Wednesday: "Parliament has been considering Brexit for months and years.
"It has had the opportunity to make whatever legislative provisions it has wished over that period and it has, in fact, made a plethora of legislative provisions - including and starting with the authorisation of the giving of the Article 50 notice."
Sir James told the hearing: "Parliament had the opportunity, if it had wished to do so, to legislate not merely to control the perceived undesirable consequences of a no-deal Brexit.
"It could have said, and by the way, if and to the extent Parliament is going to be prorogued next week, we think we need more time. But it didn't do that."
Mr Johnson says the five-week suspension is to allow the Government to set out a new legislative agenda in a Queen's Speech when MPs return to Parliament on October 14.
But those who brought legal challenges against the Prime Minister's decision argue the prorogation is designed to prevent parliamentary scrutiny of the UK's impending exit from the EU on October 31.
The court, which is sitting as a panel of 11 justices for only the second time in its 10-year history, must reconcile contradictory judgments issued by the English and Scottish courts.
The High Court in London dismissed the case brought by businesswoman and campaigner Gina Miller, finding that the length of the prorogation was "purely political".
But the Inner House of the Court of Session in Edinburgh ruled that Mr Johnson's decision was unlawful because "it was motivated by the improper purpose of stymying Parliament".
On the first day of the hearing on Tuesday, Mrs Miller's barrister Lord Pannick QC argued that Mr Johnson's motive for an "exceptionally long" prorogation was to "silence" Parliament, and that his decision was an "unlawful abuse of power".
A cross-party group of around 75 MPs and peers, led by SNP MP Joanna Cherry QC, was responsible for the Scottish challenge and the appeal against the Court of Session's decision is being brought by the Advocate General for Scotland, Lord Keen QC, on behalf of the Westminster Government.
Lord Keen submitted that the courts "must not cross the boundaries and intrude upon the business of Parliament", and confirmed Mr Johnson will comply with the Supreme Court's ruling if it finds his decision was unlawful.
On Wednesday, Sir James Eadie QC, representing Mr Johnson, argued the Supreme Court has no jurisdiction to rule on the lawfulness of the length of prorogation, followed by submissions from Aidan O'Neill QC for Ms Cherry.
Victims' campaigner Raymond McCord - who brought separate proceedings in Belfast, arguing that a no-deal Brexit would damage the Northern Ireland peace process - has also been given permission to intervene in the Supreme Court case, and his lawyers will address the court on Thursday.
Mrs Miller's challenge is supported by former prime minister Sir John Major, shadow attorney general Baroness Chakrabarti and the Scottish and Welsh governments, who are all interveners in the Supreme Court case and will also be heard on Thursday.
Mr Johnson advised the Queen on August 28 to prorogue Parliament for five weeks and it was suspended on September 9.
The justices will continue to hear submissions from the parties and interveners on Thursday, the third and final day of the hearing, but it is not yet known when they will give a ruling.
During a brief discussion on Wednesday about what order the court should make in the event it concludes the prorogation was unlawful, Lord Reed said the issue could be a "very difficult question" for the judges.