Boris Johnson is the "the father of lies" who shut down "the mother of parliaments", the UK Supreme Court has been told.

Eleven Supreme Court justices heard from both sides on Wednesday as they prepare to rule on if the Prime Minister's five-week suspension of parliament was lawful.

The historic legal case was brought after the Court of Session in Edinburgh dramatically ruled last week that Johnson's government had acted illegally.

Lawyers arguing against the government said the PM acted in "bad faith" when he claimed the reason for the suspension - also known as prorogation - was to allow for a new Queen's Speech, and was not to do with Brexit.

But Sir James Eadie QC, representing the Prime Minister, told the panel the suggestion that prorogation was for any "improper purpose" or to "stymie" Parliament was "untenable".

The Supreme Court is hearing appeals on two separate challenges in the English and Scottish courts over the prorogation, with the High Court in London ruling in favour of the government last week.

Urging the justices to reject the government's appeal in the Scottish case, Aidan O'Neill QC, representing the group of politicians who brought the case, called on the court to "stand up for truth".

He continued: "Stand up for reason, stand up for diversity, stand up for parliament, stand up for democracy by dismissing this government appeal and upholding a constitution governed by laws, not the passing whims of men.

"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."

Mr O'Neill said documents provided in the Court of Session case contradicted the PM's public reason for proroguing parliament, which Johnson claimed would allow his government to set out a new legislative agenda in a Queen's Speech when MPs return to parliament on October 14.

He said the papers - including a memo to the Prime Minister on prorogation and Johnson's handwritten response - showed that "the true dominant purpose of prorogation was, as the inner house (of the Court of Session) correctly observed, to stymie parliamentary scrutiny of the executive regarding Brexit".

He concluded the suspension of parliament "was for an improper purpose and done in bad faith."

The Prime Minister advised the Queen on August 28 to prorogue Parliament for five weeks and it was suspended on September 9.

Representing the government, Sir James told the court: "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."

He also said decisions to prorogue Parliament "are inherently and fundamentally political in nature" and not a matter for the courts.

However, during an exchange with Lord Reed, one of the justices hearing the case, he accepted there are limits to the government's prerogative power.

Sir James conceded is part of the court's role to determine what those limits are and whether they have been exceeded.

Lord Pannick, representing campaigner and businesswoman Gina Miller against the government, argued on Tuesday that Mr Johnson's motive for an "exceptionally long" prorogation was to "silence" Parliament, and that his decision was an "unlawful abuse of power".

Ms Miller's action is supported by former prime minister Sir John Major, shadow attorney general Baroness Chakrabarti and the Scottish and Welsh governments, who will all give submissions to the Supreme Court on Thursday.

It will be the final day of the three-day hearing, but it is not yet known when the court will give a ruling.