The Queen would dismiss Boris Johnson as prime minister if he refused to comply with a law requiring him to seek an extension to Brexit talks, leading Remainer Dominic Grieve has said.
The former attorney general said the PM would be “out in five minutes” if he tried to defy a Supreme Court order to go to Brussels.
Mr Grieve said he expected current attorney Geoffrey Cox and lord chancellor Robert Buckland would resign, while the civil service would withdraw co-operation with a prime minister openly flouting the law in this way.
A cross-party group of anti-no deal MPs passed legislation known as the Benn Act, earlier this month,which requires Mr Johnson to seek an extension to the Article 50 Brexit extension, delaying the date of withdrawal to the end of January, if he has not secured parliamentary approval for a deal or a no-deal outcome by 19 October.
Mr Johnson has branded the legislation a “surrender act” and insists that despite its provisions he will not ask Brussels for an extention beyond the scheduled Brexit date of 31 October.
But Mr Grieve said that would lead to an instant legal challenge which would reach the Supreme Court within days, where judges would issue a rarely-used order known as “mandamus” requiring a public official to carry out a non-discretionary responsibility.
“He would be taken to court and a writ of mandamus would be issued against him and he would be told that he had, as a matter of law, to write the letter,” Mr Grieve told Sky News.
“I suspect the courts could deal with it very quickly.”
Mr Grieve added: “At that stage, the cabinet secretary and civil service will refuse to work for him. I assume the attorney general and lord chancellor would have resigned, because it is such a flagrant breach of the law.”
Even though Mr Cox has been a vocal supporter of Mr Johnson’s approach to Brexit, Mr Grieve said he was “a good enough lawyer to know you can’t support a prime minister who is breaking the law of the land”.
Pressed on whether Mr Johnson would face further legal action if he refused to comply with the court order, Mr Grieve said: “There is no question of putting the prime minister on trial.
“The Supreme Court - Her Majesty’s judges - telling the prime minister that as a matter of law he has to do something? He will be gone in five minutes. He will be dismissed.”
Asked if it was the Queen who would dismiss Mr Johnson in these circumstances, Mr Grieve replied simply: “Yes.”
The former attorney general insisted that it was a “hypothetical position”, but added: “If he intends to continue behaving in this completely ludicrous fashion, yes, perhaps.”
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