Rory Stewart has told Sky News around a dozen Conservative MPs could rebel against the government next month as part of opposition moves to stop a no-deal Brexit on 31 October.
The former Tory leadership candidate said MPs should on Tuesday be introducing legislation to block the UK from leaving the European Union without an agreement and instead force an extension.
The UK will exit the bloc at the end of October “do or die”, according to Boris Johnson who has insisted he is still working hard to reach an agreement with the EU.
Parliament returns on Tuesday after its summer break and the prime minister’s opponents know they do not have much time to fight back before it is suspended – or prorogued – the week after for up to five weeks until 14 October.
Mr Johnson is now facing attempts by his parliamentary opponents to legislate against a no-deal.
Labour’s deputy leader Tom Watson has said a bill has already been drafted.
He said: “I have taken advice on legislative solutions to challenge the prime minister’s action to stop us crashing out of the EU without a deal. I am in discussion with colleagues in other parties and a bill to achieve this outcome has been drafted.”
Mr Stewart confirmed to Sky News: “I’ve seen the contents of it and we can do it.”
Asked if he was prepared to go against his party if he thought it was in the national interest, he replied: “Yes to stop a no-deal Brexit.
“I’m a proud Conservative, I support the Conservative Party. I just think a no-deal Brexit would be a huge mistake and I have to stop it happening.”
Asked how many of his colleagues would rebel, he said: “Maybe a dozen but that will be enough. There is only a majority of one at the moment.”
Labour leader Jeremy Corbyn said next week was the “last chance” to stop a no-deal Brexit.
At an event in Glasgow, he said: “Yes, it is the chance and we will do absolutely everything we can to prevent a no-deal Brexit and the prime minister taking us into the hands of Donald Trump and a trade deal with the USA.
“That is the real agenda of the prime minister. There is a lot of work being done in preparation for next Tuesday.”
Parliament will be prorogued in the week beginning 9 September until 14 October – the day of the Queen’s Speech.
Mr Johnson’s opponents have claimed the move was aimed at reducing Commons debating time to restrict MPs’ ability to block a no-deal.
But the prime minister has insisted his rivals could be making the prospect of a withdrawal from the bloc without an agreement more likely.