Prime Minister Boris Johnson’s decision to suspend Parliament for five weeks “is not a matter for the courts”, the High Court has ruled.

Giving their reasons for rejecting the case brought by businesswoman Gina Miller, leading judges said the decision to prorogue Parliament was “purely political” and therefore not capable of challenge in the courts.

Ms Miller’s claim – which was supported by former prime minister Sir John Major, shadow attorney general Baroness Chakrabarti and the Scottish and Welsh governments – was dismissed last Friday.

Lord Chief Justice Lord Burnett, Master of the Rolls Sir Terence Etherton and President of the Queen’s Bench Division Dame Victoria Sharp delivered their ruling at a brief hearing in London on Wednesday.

In their judgment, they stated: “We concluded that the decision of the Prime Minister was not justiciable (capable of challenge). It is not a matter for the courts.”

They added: “The Prime Minister’s decision that Parliament should be prorogued at the time and for the duration chosen and the advice given to Her Majesty to do so in the present case were political.

“They were inherently political in nature and there are no legal standards against which to judge their legitimacy.”

They said it was “impossible for the court to make a legal assessment of whether the duration of the prorogation was excessive by reference to any measure”.

The court also said that legislation passed by Parliament, which requires Mr Johnson to seek an extension to the current Brexit deadline of October 31 if no deal is reached with the EU, had “undermined” Ms Miller’s case.

The judgment stated: “The ability of Parliament to move with speed when it chooses to do so was illustrated with clarity and at the same time undermined the underlying premise of the cases advanced by both the claimant and the interveners, namely that the prorogation would deny Parliament the opportunity to do precisely what it has just done.”

The High Court’s reasons were issued shortly after the Court of Session in Edinburgh ruled that Mr Johnson’s suspension of Parliament was unlawful.

The English and Scottish proceedings, along with a similar case being heard in Belfast, are expected to be considered together by the Supreme Court in London, with the hearing due to start on September 17.

At the hearing last week, Ms Miller’s barrister, Lord Pannick QC, had argued that Mr Johnson’s advice to the Queen to suspend Parliament for five weeks was an “unlawful abuse of power”.

Lawyers representing Mr Johnson said Ms Miller’s claim was “academic” and urged the court to reject it.

Speaking outside the Royal Courts of Justice after the ruling last week, Ms Miller said she was “very disappointed with the judgment”.

“To give up now would be a dereliction of our responsibility. We need to protect our institutions,” she said.

“It is not right that they should be shut down or bullied, especially at this most momentous time in history.

“My legal team and I will not give up our fight for democracy.”