Boris Johnson will call for a general election on 15 October if Labour and rebel Tories succeed in blocking a no-deal Brexit.
He challenged Jeremy Corbyn to put his policy of “dither and delay” over EU withdrawal to the British people.
Mr Johnson needs the support of two-thirds of MPs to trigger an election.
But shadow Brexit secretary Sir Keir Starmer told Labour MPs the leadership would not back an election until a delay had been agreed with the EU.
Chancellor Sajid Javid has presented his spending plan to MPs in the Commons, with the health service, education and the police expected to fare well.
He told MPs the government had “turned the page on austerity”, outlining £13.8bn of investment on areas including health and education.
Mr Javid said it was the fastest spending increase for 15 years, but the shadow chancellor, John McDonnell, accused him of “meaningless platitudes”.
Meanwhile, No 10’s decision to expel 21 Tory MPs for defying the party whip on Tuesday continues to causes recriminations in the party.
One of those booted out of the party, Margot James, has publicly questioned the role played by Dominic Cummings, the PM’s senior aide, in the decision.
Raising the issue at PMQs, she urged Mr Johnson to bear in mind his predecessor Margaret Thatcher’s famous adage that “advisers advise and ministers decide”.
And in Scotland, a judge has rejected a bid to have Mr Johnson’s plan to shut down Parliament ahead of Brexit declared illegal.
The showdown between the government and opponents of a no-deal Brexit will continue later as Labour and other opposition parties seek to pass a bill requesting a further delay if there is no deal by 19 October.
A total of 21 Tories defied the PM on Tuesday to vote with the opposition to enable the bill to be considered, as Mr Johnson suffered his first Commons defeat as prime minister by a margin of 328 votes to 301.
Speaking at Prime Minister’s Questions, Mr Johnson said it was “absolutely clear” that the UK would get a new deal from Brussels, with the controversial Irish backstop removed.
He suggested that Mr Corbyn was afraid of the judgement of the people, joking that “there is only one chlorinated chicken I can see this House and he is on that bench”.
But the Labour leader said the PM was “running down the clock” on a no-deal Brexit and “hiding the facts” about the likelihood of food and medicine shortages.
“I don’t see how I can be accused of undermining the negotiations because there are no negotiations taking place,” he told MPs.