Boris Johnson's thinking when he signed the Brexit Withdrawal Agreement is not a matter for judicial scrutiny, the High Court ruled on Wednesday.
he Prime Minister faced a legal challenge from a border citizen in Northern Ireland over claims that he never intended to comply with the terms of the UK's departure from the European Union.
Lawyers for the woman, granted anonymity and referred to as JR83, alleged that Mr Johnson acted in bad faith when he put pen to the treaty back in January.
But dismissing the challenge, Mr Justice McAlinden held: "The court really has no constitutional role or function in delving into the mindset of the Prime Minister at the time he signed the Withdrawal Agreement."
The case came before the High Court in Belfast a day after the UK Government signaled it would drop controversial clauses within legislation which had implications for the Irish border.
Barry Macdonald QC, representing JR83, insisted proceedings were not directed at the Internal Markets Bill.
Instead, counsel argued, it was about how the Prime Minister allegedly never planned to stick to the terms of the EU (Withdrawal Agreement) Act passed by Parliament.
"He was privately planning to take a different course," Mr Macdonald said.
According to the barrister Mr Johnson signed up to the treaty to secure the UK's exit from the EU for "improper collateral purposes".
He added: "The uncontroverted evidence at the moment does seem to suggest he was acting in bad faith."
Tony McGleenan QC, for the Prime Minister, countered that the case was rendered academic by the UK Government's move to withdraw parts of the Internal Markets Bill.
Concerns about possible non-implementation of the Northern Ireland Protocol, aimed at ensuring no hard border with the Republic of Ireland, have been proven "entirely unfounded", he claimed.
Mr McGleenan argued that issues of foreign policy and Mr Johnson's actions in signing the agreement should not be subjected to judicial scrutiny.
"He executed the will of Parliament, therefore that's a sovereign act," the barrister said.
"It's not for the court to seek to engage in some sort of psychological enquiry into the state of the Prime Minister's mind."
Backing those submissions, Mr Justice McAlinden refused leave to seek a judicial review.
"(The Prime Minister's) subsequent actions could be open to interpretation in terms of whether at that time he was fully aware of the requirements set out in the Withdrawal Agreement, and was unhappy with those requirements and intended at that stage to bring about a situation whereby the UK would not be required to comply with those requirements in domestic law," the judge said.
"It could be the case that such a state of knowledge only occurred to the Prime Minister and the Prime Minister's team thereafter, and it was in light of subsequent developments that the UK Government took the view it would not be in a position to comply with the international treaty obligations set out in the Withdrawal Agreement and, as a result of that, decided to enact the Internal Markets Bill.
"But these issues are really not issues for this court to adjudicate upon or to determine."
He also acknowledged that issues about implementation of the Northern Ireland Protocol and avoiding a hard border "appear to have been addressed."
The judge added: "The core complaint of the applicant has been apparently met by the UK Government, therefore this claim for judicial review is to a large extent academic."