The Queen risks being drawn into the bitter Brexit battle, experts warned after Tory leadership contender Dominic Raab said he would be prepared to suspend Parliament to ensure the UK leaves the EU.
The former Brexit secretary refused to rule out proroguing Parliament – bringing an end to the session – to prevent MPs blocking the UK's withdrawal.
Formally it is the monarch who prorogues Parliament and asking the Queen to endorse such a move would create a constitutional crisis.
Hardline Brexiteers have suggested prorogation could be used as a mechanism to prevent MPs blocking a no-deal exit from the European Union on October 31.
But critics said the approach would be "a coup against Parliament" and Tory leadership contender Matt Hancock called on all his rivals to rule it out.
In the Commons, Speaker John Bercow insisted he would not allow MPs to be sidelined.
"Parliament will not be evacuated from the centre stage of the decision-making process on this important matter," he said.
"That's simply not going to happen."
Commons Leader Mel Stride, who is backing Michael Gove for the leadership, said: "I do think that Her Majesty should be kept out of the politics of our Parliament, and I am sure that will be a matter that will be at the forefront of those who toy with those decisions in the future."
Parliamentary expert Hannah White, deputy director of the Institute for Government, said the move "would amount to a coup against Parliament and risk bringing the Queen into a terrible conflict".
She added: "The implication of Raab's refusal to rule out this strategy is that he thinks it would potentially be legitimate to suspend Parliament, not simply to let the Article 50 clock run down but to prevent MPs from making a decision he knows they would want to take.
"This would be extremely controversial, particularly in these circumstances because the Government does not have a majority.
"Asking the Queen to give effect to this strategy would draw her into a massive political debate – something which Number 10 and the Palace are normally at great pains to avoid."
Dr White suggested that Buckingham Palace "would look for ways to limit the Queen being drawn into the process", possibly by delaying long enough to allow Parliament the opportunity to prevent prorogation.
One way could be through a no confidence motion to bring down the Government.
She said: "The effect of attempting to prorogue Parliament to pursue a no-deal policy to which it has thus far been firmly opposed would likely be to prompt an election. That may even be the intention."
Health Secretary Mr Hancock wrote to his rivals, saying: "To suspend Parliament explicitly to pursue a course of action against its wishes is not a serious policy of a prime minister in the 21st century.
"What kind of message would this send around the world about our values when so many have given so much for the rights of democratic freedom?"
Leadership contender Rory Stewart said proroguing Parliament would be "unlawful, undemocratic, and unachievable" and "the idea itself is profoundly offensive to our liberty, constitution and traditions".
Mr Raab's stance on the issue became clear at a hustings organised by the One Nation group of centrist Tories on Wednesday.
Work and Pensions Secretary Amber Rudd, a leading player in the One Nation group, said: "I think it's outrageous to consider proroguing Parliament. We are not Stuart kings."
But a supporter of Mr Raab said: "Dominic made clear that he would use every lever of the executive to ensure that the UK can leave the EU at the end of October."
Ruling out a no-deal Brexit or seeking an extension beyond October 31 meant "weakening our negotiating leverage in Brussels", the source said.