Prime Minister Boris Johnson was under fire Thursday from his own Tory MPs and the embarrassing prospect of an investigation into whether he lied to parliament over the Partygate scandal.

British legislators have agreed to launch a probe by a parliamentary committee into Johnson's denials to the House of Commons of breaking the law by undermining the nationwide lockdown his government imposed by partying in Downing Street, which has drawn public outrage and caused his own MPs to turn on him.

The committee's investigation will kick off once the London police have finished their own probe and an internal report regarding the scandal is published in full.

Debating ahead of the vote, several members of Johnson's own Conservative party put ranks aside to criticize his behavior and highlighted that they no longer backed him.

Johnson's premiership is unprecedented, as he is the first British leader to be fined for breaking the law after he became the first UK leader to be penalized for breaking the law when police disclosed that they had issued dozens of penalty notices to his employees as part of an ongoing investigation.

Penalties for additional events, though, could follow, after opposition parties called on parliament's cross-party "privileges committee" to examine Johnson.

If lawmakers are found guilty of offenses, it has the authority to discipline them, including suspending them from the Commons.

The probe prompted one junior minister to resign, while senior Tory MP Mark Harper told parliament earlier this week that Johnson was "no longer... worthy" of being prime minister. 

Johnson had repeatedly denied before the house that he or his staff had breached the strict lockdown his government had put in place, though fines issues last week have proven his claims to be false. He did apologize for the scandal, though remained adamant he never knowingly misled parliament and vowed to press on with other issues, including the war in Ukraine.

The premier had previously stressed that accepting a fine did not mean he broke the law. His allies also revealed that he would not resign were the Met to fine him.

According to a recent nationwide poll, over two-thirds of the public viewed Johnson badly, compared to only 16% positively, with the term "lie" being the most often used response.

When media reports about Downing Street parties initially appeared, business minister Paul Scully admitted that the government "didn't handle it especially effectively at that moment, communication-wise."