Phillip Lee sat on the opposition benches on Tuesday | U.K. Parliament Boris Johnson loses majority as MPs seek to stop no-deal Brexit Phillip Lee defected, accusing the Tories of using ‘political manipulation, bullying and lies.’

LONDON — The governing Conservative Party lost its majority on Tuesday as one of its MPs defected to join the anti-Brexit Liberal Democrats.

The defection was the opening gambit in an acrimonious debate as British MPs sought to prevent Prime Minister Boris Johnson from taking the U.K. out of the European Union without a deal.

Phillip Lee sat on the opposition benches the prime minister stood to deliver a statement in the House of Commons and accused the Tories of deliberately using “political manipulation, bullying and lies” to push through its plans on Brexit.

The move increases pressure on Johnson, whose majority was already looking shaky, but does not automatically trigger an election because that would require a separate vote.

The debate in the House of Commons, presided over by the Leader of the House of Commons Jacob Rees-Mogg, played out as a battle between those who believed parliament had a solemn duty to intervene to prevent a no-deal Brexit; and those who believed parliament had a solemn duty to ensure Brexit took place without further delay. Both invoked the will of the people and cast themselves as their protectors.

MPs hope to force the prime minister to delay Brexit by changing the law to require him to seek an extension from Brussels if no exit deal has been agreed between the U.K. and the EU by next month's European Council meeting.

It is expected the government will put forward a motion calling for an election late Tuesday, with a vote Wednesday. This would need the backing of two thirds of MPs to trigger a snap election.

“The prime minister has been very clear that should MPs tonight vote to trash the U.K.’s negotiating position, hand power over to the opposition then the next logical step for the prime minister — which he doesn’t want — would be via the Fixed Term Parliaments Act [to call] for an election and then the British public will decide who goes to Brussels to make that decision,” a No. 10 spokesperson said.

However, to clear the Commons vote Labour would need to back the motion and the party's position was unclear for much of the day. Labour leader Jeremy Corbyn has repeatedly called for an election, but now fears Johnson could set the national poll for a date later than the October 31 Brexit deadline, meaning the U.K. might quit the EU without a deal during the campaign.

As MPs debated, Labour's Shadow Foreign Secretary Emily Thornberry said the party would not vote for a general election before a no-deal Brexit has been taken off the table.

“There won’t be a general election tomorrow, because we’re not going to vote for it, because we have to make sure this legislation is been embedded [and] signed off by the queen,” Thornberry said.

“We want a general election but we want to get this legislation done first,” she added. “It’s a question of getting the sequence right. First we stop no-deal, then Boris is going to send us all away and not let us come back for a while. But when we come back we will see what happens then.”

At a meeting of Labour MPs and peers in the Palace of Westminster, chief whip Nick Brown said the party would not fall into a general election “trap,” according to those who were in the room.

Lloyd Russell-Moyle MP said the meeting was about “making sure that we don’t fall into the elephant trap” of allowing the prime minister to lead the country into a no-deal Brexit. He added: “We are dealing with some very dark forces.”

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