Boris Johnson’s advice to the Queen to suspend Parliament for five weeks was an “unlawful abuse of power”, leading judges have heard.
The claim was made on Thursday at the start of the latest legal challenge to the Prime Minister’s move.
Lord Chief Justice Lord Burnett, sitting with two other judges at the High Court in London, is being urged to make a declaration that the decision taken on August 28 to advise the Queen to prorogue Parliament was unlawful.
The urgent judicial review application to contest the Prime Minister’s decision has been brought by businesswoman Gina Miller, who successfully challenged the Government at the High Court in 2016 over the triggering of the Article 50 process to start the Brexit countdown.
The decision is set to be announced on Friday.
Her case is supported by a number of other parties, including former prime minister Sir John Major.
The action is being contested by the Prime Minister, whose lawyers will argue that the advice given to the Queen was not unlawful.
Lord Pannick QC, representing Ms Miller, told the judges: “The prorogation is timed to occur at a period of acute political crisis, with the UK scheduled to leave the European Union on 31 October 2019 but with no agreement having been concluded between the UK and the EU on the terms of its withdrawal.
“The claimant submits that the effect of the prorogation, when time is of the essence in the lead-up to the 31 October 2019 deadline, has the effect of seriously impeding the exercise of Parliament’s functions, as the Prime Minister well knew.
“There is no justification for closing Parliament in this way and, accordingly, it represents an unjustified undermining of parliamentary sovereignty which is the bedrock of our constitution.”
He added: “Our case is that the Prime Minister’s advice to Her Majesty to prorogue Parliament for a period of five weeks is an unlawful abuse of power.”
Lord Pannick told the Lord Chief Justice, sitting with Master of the Rolls Sir Terence Etherton and President of the Queen’s Bench Division Dame Victoria Sharp: “The Prime Minister’s decision to prorogue Parliament is contrary to constitutional principle and constitutes an abuse of power.”
The hearing in London comes the day after Mr Johnson fought off a similar action in Scotland.
A judge at the Court of Session in Edinburgh ruled on Wednesday that the planned prorogation was lawful – that decision is now being appealed against.
Whatever the outcome of the challenges against the decision to prorogue Parliament, it is likely that the dispute will end up at the UK’s highest court.
A spokeswoman for the Supreme Court in London has said “should any parties choose to appeal to the UK Supreme Court following the prorogation appeal hearings in the lower courts”, the court has set aside September 17 “as a date to hear such an appeal”.