British Prime Minister Boris Johnson's Conservative Party lost its parliamentary majority Tuesday after a member of parliament defected to the Liberal Democrats.

Phillip Lee, a 27-year veteran of the House of Commons, announced Tuesday that he would be leaving the governing party to join the anti-Brexit Liberal Democrats. He subsequently crossed the House to sit with his new party.

Watch: Conservative MP Phillip Lee defects to the Liberal Democrats, crossing the House of Commons during a speech by Boris Johnson



His move means the prime minister has no working majority ahead of a crucial #Brexit vote



[tap to expand] https://t.co/vi78s0o5JA pic.twitter.com/CfnKNm0pJ8 — BBC Politics (@BBCPolitics) September 3, 2019

Lee said his decision was prompted in large part by the Conservative Party's support of the United Kingdom's exit from the European Union, whether a deal is reached or not.

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"This Conservative Government is aggressively pursuing a damaging Brexit in unprincipled ways. It is putting lives and livelihoods at risk unnecessarily and it is wantonly endangering the integrity of the United Kingdom," Lee said in a statement.

"More widely, it is undermining our country’s economy, democracy and role in the world. It is using political manipulation, bullying and lies. And it is doing these things in a deliberate and considered way. It has gone so far beyond reckless as to cease to be conservative," he added.

Lee's defection ramps up the pressure on Johnson, whose promise to follow through on Brexit by Oct. 31 has drawn sharp criticism.

Lee is the third member of parliament to join the Liberal Democrats in recent months, bringing their count up to 15 out of the 650 seats in the House of Commons.

Liberal Democrat leader Jo Swinson thanked Lee for joining her party "at the most crucial time."

"I look forward to working with you to prevent a disastrous Brexit, and to fight for a fairer, more equal society," she said.