Boris Johnson’s government is unworthy of trust because it conspired to ensure that “the mother of parliaments” was closed down by “the father of lies”, the supreme court was told in an impassioned speech by a Scottish advocate.

In combative closing comments, Aidan O’Neill QC called on the 11 justices hearing the prorogation case to reject legal arguments advanced by the government that the courts do not have the power to intervene in the decision to prorogue parliament for five weeks.

His speech was delivered at the end of the second day of the emergency hearing at the UK’s highest court into whether the prime minister’s advice to the Queen to suspend debates at a time of a national constitutional crisis over Brexit was lawful.

“What we have with this prorogation is the mother of parliaments closed down by the father of lies,” declared O’Neill, who had won his claim in the Scottish courts. “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 the power of prorogation which has been entrusted to the government.

Q&A What is the UK supreme court and how does it work? Show Hide The supreme court of the United Kingdom was formally established on 1 October 2009. It is the ultimate court for hearing cases of the greatest public or constitutional importance, and is the final court of appeal in the UK, except for criminal cases heard in Scotland. The supreme court took over the judicial functions of the House of Lords, separating the judiciary from the legislature. It brought an end to the system of appealing to the "lords of appeal in ordinary" - commonly known as the law lords. The court comprises the president and deputy president and 10 other judges of the supreme court. Judges are appointed by the Queen on the advice of the prime minister, to whom a name is recommended by a special selection commission. The prime minister is obliged to recommend this name. The judgments in all decided cases from the court are published on the court's website.

“This government has proved itself unworthy of our trust as it uses the power [of its] office ... which is corrosive of the constitution and destructive of the system of parliamentary democracy on which our union polity is founded. Enough is enough. Dismiss this appeal and let them know that. This is what truth speaking to power sounds like.”

In contrast with other lawyers who addressed the supreme court this week through detailed reference to past cases and subsections of legislations, O’Neill adopted a centuries-long historical perspective and an emotive approach to the nature of the UK’s constitution.

Urging judges not to make this a “Dred Scott moment” – referring to the landmark 1857 US supreme court case that affirmed slave owners’ rights and paved the way to the civil war – O’Neill urged the court to “stand up for truth, stand up for reasons, stand up for unity in diversity, stand up for democracy”.

The justices should dismiss the government’s appeal against the ruling by the inner house of Scotland’s court of session by “upholding a constitution governed by laws not by the passing whims of men”, he said.

The UK was a parliamentary representative democracy, O’Neill said, where the executive was subordinate to the law and accountable to parliament. Unlike in the US, the executive was not elected directly by the people. Parliamentary democracy was the “animating principle of the UK constitution”, he said.

His opening flight of oratory, lasting half an hour – during which he was barely interrupted by the justices – took in the 1314 battle of Bannockburn, Macbeth, the German constitutional court in Karlsruhe, Oliver Cromwell and Nelson Mandela. The UK was a “state of nations” rather than a single nation state, O’Neill suggested.

He dismissed the government’s claim that parliament had the power to resist prorogation. Under the rules in the parliamentary handbook, Erskine May, O’Neill said, MPs could vote to remain in session but required assent for it to become effective in law – something which ministers would withhold.

Inappropriate for judges to intervene in prorogation, says government lawyer Read more

Even if the government had neither intended to avoid parliamentary scrutiny nor acted in bad faith, O’Neill continued, “their ignorance of our constitution does not make what they have done lawful. That’s why the effect [of closing down parliament] is what’s significant …”

Downing Street officials had looked at their diaries and found the largest period of time permitted under legislation to close down the Commons, he said. “They have seen a black hole and leapt in,” O’Neill said. “It’s clever-clever perhaps, but is it constitutional?”

The phrase “royal prerogative”, frequently deployed by government lawyers, covered a bundle of unrelated residual powers and was not a “magic” word that could obstruct accountability to parliament, the judges were told.

Earlier in the day Sir James Eadie QC, representing Boris Johnson’s government, argued there were areas of political process and “high policy” that could not be subjected to any judicial standards. It was constitutionally inappropriate for the courts to intervene in the prime minister’s decision to prorogue parliament because there was a clear separation of powers, he told the court.

Eadie said the only “sure and proper guide” for courts to intervene in cases was on the basis of already enacted legislation. Otherwise, he said, it moved the courts into the territory of “parliamentary controversy”.

There were a “myriad of reasons for the length of this prorogation”, Eadie said. “Reading [Cabinet Office] documents the evident aim was everyone was concerned to get to a place where a Queen’s speech was produced.”

In written submissions, Lord Garnier QC, representing the former prime minister John Major, said it would be remarkable if the courts took the view “that there is nothing in law to prevent a prime minister from proroguing parliament in any circumstances or for any reason”.

He added: “The fact that there are constitutional safeguards which operate on the well-intentioned [prime minister] is no reason for the courts to reject any possibility of intervening even in other cases.”

The supreme court case has generated widespread interest. The first members of the public began queueing at 6.30am on Wednesday to secure a seat in court. The livestreamed broadcast of the proceedings had attracted more than 4m requests to view during the course of Tuesday morning’s hearing.

The hearing continues.

• This article was amended on 19 September 2019 because an earlier version incorrectly referred to “Hamlet’s Macbeth” when Shakespeare’s Macbeth was meant.