Boris Johnson is considering seeking an early general election if MPs wanting to block a no-deal Brexit defeat the government this week.
The BBC understands "live discussions" are going on in No 10 about asking Parliament to approve a snap poll.
Political editor Laura Kuenssberg said it could happen as soon as Wednesday but no final decision had been taken.
Tory ex-ministers are joining forces with Labour to stop the UK leaving the EU on 31 October without a deal.
Amid mounting speculation about an election, Mr Johnson is due to hold an unscheduled cabinet meeting at 17.00 BST and will also speak to Conservative MPs on Monday afternoon.
BBC
Russia's unmanned Luna-25 spacecraft has crashed into the Moon after spinning out of control, officials say.
Donald Trump has confirmed that he will not take part in Republican presidential debates with his rivals in the race for the White House.