Conservative MP Philip Lee has defected to the Liberal Democrats ahead of a showdown between Boris Johnson and Tory rebels over Brexit.
Mr Lee, the MP for Bracknell, took his seat on the opposition benches as the PM addressed the Commons.
His defection means that Boris Johnson no longer has a working majority in the Commons.
He said the government was “pursuing a damaging Brexit in unprincipled ways”, putting lives and livelihoods at risk.
Speaking in the Commons, Mr Johnson told MPs he wanted a negotiated exit from the EU and insisted there was “real momentum” behind the talks.
But he said plans by rebel Tory MPs to pass legislation effectively blocking a no-deal exit on 31 October would “destroy any chance of negotiating a new deal”.
If the rebels succeeded in their aims, he said it would force him to go to Brussels to “beg for another pointless delay” to Brexit and he would “never” do that.
“It is Jeremy Corbyn’s surrender bill. It means running up the white flag,” he added.
Before Mr Lee’s defection, Mr Johnson only had a working majority of one in the Commons.
In a letter to the prime minister, Mr Lee said the Conservative Party “had become a narrow faction in which one’s Conservatism is measured by how recklessly one wants to leave the European Union”.
