Former prime minister Sir John Major has told the BBC he would seek a judicial review in the courts if the new prime minister tried to suspend Parliament to deliver a no-deal Brexit.
Sir John said such a move would be “utterly and totally unacceptable”.
Using a judicial review, anyone can apply to challenge the lawfulness of decisions made by the government.
Boris Johnson – the frontrunner in the Tory leadership race – has refused to rule out proroguing Parliament.
A source close to Boris Johnson told the BBC’s assistant political editor Norman Smith that Sir John “has gone completely bonkers” and had “clearly been driven completely mad by Brexit”.
They said the threat of court action was “absurd” and risked dragging the Queen into politics.
The UK had been due to leave the EU on 29 March, but this date was delayed after MPs repeatedly rejected Theresa May’s deal. Currently, the date for exit is 31 October.
If that date is reached without a deal being agreed on the separation process, then the UK will leave without one.
MPs have consistently voted against this option, but the prime minister could try to get around that by closing Parliament – proroguing – in the run-up to Brexit day, denying them an opportunity to block it.
The question of prorogation was raised during a lTV debate between Mr Johnson and his rival in the race to lead the Conservative Party Jeremy Hunt.
Mr Hunt categorically ruled it out but Mr Johnson said he would “not take anything off the table”.
Speaking to Radio 4’s Today programme, Sir John said: “In order to close down Parliament, the prime minister would have to go to Her Majesty the Queen and ask for her permission.”
He said it would be “inconceivable” the Queen would refuse his request and the she would be put “amidst a constitutional controversy”.
“The Queen’s decision cannot be challenged in law, but the prime minister’s advice to the Queen can, I believe, be challenged in law – and I for one would be prepared to seek judicial review to prevent Parliament being bypassed,” he said.
Sir John also criticised the “artificial” Brexit deadline of 31 October which he said “had a great deal more to do with the election of leader for the Conservative Party than the interests of the country”.
“National leaders look first at the interests of the country – not first at the interests of themselves,” he added.