Boris Johnson will seek a general election later if Labour and rebel Tories succeed in seeking to block a no-deal Brexit on 31 October.
The PM has said he will not accept another Brexit delay but a bill forcing him to seek an extension if there is no deal is set to be approved by MPs.
He needs two-thirds of MPs to trigger an election, but Labour and other parties won’t back it at this stage.
The decision to expel 21 Tory rebels has caused recriminations in the party.
The group of senior former ministers, including ex-chancellors Philip Hammond and Ken Clarke, have insisted they put the national interest ahead of their own.
But minister Kwasi Kwarteng said it was right the MPs had had the whip withdrawn, as they could not oppose the government on “the key policy issue of the day”.
On another day of high drama in Westminster, Boris Johnson will face his first session of Prime Minister’s Questions after losing his Commons majority on Tuesday.
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 as Mr Johnson suffered his first Commons defeat as prime minister by a margin of 328 votes to 301.
If the Brexit delay bill passes later on and moves to the Lords, as is expected, Mr Johnson will push for an immediate vote on an early general election.
After Monday’s defeat, he told MPs he had no choice but to press ahead with efforts to call an October election, adding: “The people of this country will have to choose.”
But Labour say this is a “trap” and it will only agree to a poll – which it is understood No 10 plans for 15 October – once the chance of a no-deal Brexit next month has been ruled out.
Shadow Brexit Secretary Sir Keir Starmer told BBC Radio 4’s Today that Labour wanted a general election but “on its terms not Boris Johnson’s terms”.
He said the party did not “trust” the PM to hold the election before the Brexit deadline, as No 10 had “lied” last month when it denied reports that it planned to suspend Parliament.
“We are not shy of a general election but we are not going to be trapped into abandoning control of Parliament or be taken in what Boris Johnson says because we don’t trust him.”
Under the Fixed Term Parliaments Act, a prime minister must have the backing of at least two-thirds of the UK’s 650 MPs before a general election can be called outside of the fixed five-year terms.
The Lib Dems say they will vote against an early election at this stage while the SNP said they were ready for an election – but only after a no-deal Brexit was “taken off the table”.
