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But minister Kwasi Kwarteng said it was right the MPs had had the whip withdrawn, as they could not oppose the government on “the key policy issue of the day”.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 is facing his first session of Prime Minister's Questions after losing his Commons majority on Tuesday.
Meanwhile, a Scottish judge has rejected a bid to have Mr Johnson's plan to shut down Parliament ahead of Brexit declared illegal.
Showdown later
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…
