MPs are expected to launch a fresh attempt to block a future prime minister pushing a no-deal Brexit policy by threatening to cut off vital funds for government departments.
The cross-party plan, led by Conservative MP Dominic Grieve and senior Labour MP Dame Margaret Beckett, aims to force the future Tory leader to gain parliament's consent for leaving the EU without a deal.
Their amendment to route finance legislation in the Commons – known as "estimates" – would cut off funding for government ministries if the PM failed to do so.
Boris Johnson, the frontrunner in the race to replace Theresa May as Conservative leader, said this week the UK will leave the EU on 31 October "do or die" - heightening the risk of a no-deal scenario.
At the latest Conservative hustings, the ex-foreign secretary again refused to rule out suspending parliament to leave the EU without the consent of the Commons, but claimed the odds of a no-deal Brexit were a "million-to-one against".
But Mr Grieve, the former attorney general, told The Sun: "The suggestion that we could or should be taken out of the EU without the consent of the House of commons is fundamentally wrong, and frankly unconstitutional.
"The fact that it is being suggested as a viable option is unacceptable. The Commons should put down such markers as it can that such a course of action is unacceptable."