By Sanya Burgess and Rebecca Taylor, news reporters
The power to suspend parliament is a political matter and not for the courts to decide, the government's lawyers have argued.
Sir James Eadie has told the Supreme Court that Boris Johnson's decision to prorogue parliament is lawful and that it is not the Supreme Court's duty to interfere in political matters.
The prime minister announced in late August that he had asked the Queen to suspend parliament for five weeks until 14 October, when a new session would begin with a Queen's Speech.
The Supreme Court is examining claims from two groups who argue that Mr Johnson should not be allowed to suspend parliament for so long.
Critics who have taken their historic legal challenge to the UK's highest court of appeal claim the suspension was intended to prevent scrutiny of his belief that the UK should leave the EU by the deadline of 31 October, with or without a deal.
Mr Johnson says the suspension is to allow the government to set out a new legislative agenda in the Queen's Speech.
If Sir James's argument is accepted, any investigation by the court into issues including if Mr Johnson lied or what his motives were would be dropped.
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His case against Gina Miller convinced High Court judges a few weeks ago.
The businesswoman's case wanted the judges to find that prorogation for an "exceptional" length of time was an "unlawful abuse of power", but the court ruled suspending parliament was "inherently political in nature and there are no legal standards against which to judge the legitimacy".
However, a separate case brought by Joanna Cherry in Scotland was successful, with judges ruling the prorogation was unlawful.
The court found the suspension "an egregious case of a clear failure to comply with generally accepted standards of behaviour of public authorities".
The Supreme Court will hear submissions on her behalf this afternoon.
Speaking in court today, Sir James said in his opening remarks: "We are dealing with a prerogative power.
"It is a prerogative power that has been expressly preserved by parliament."
One justice posed the question of what would happen if a PM decided he did want to stifle the scrutiny of his actions and prorogued for a year. Sir James acknowledged the potential extreme use of it but told the court that principles shouldn't be established by being tested against the extreme.