Before the announcement in Parliament on Wednesday, the government had looked to appeal to voters on immigration and cultural issues with a raft of policy ideas, such as using the Royal Navy to stem the tide of migrants crossing the English Channel and freezing the budget of the BBC.
Yet none of those hastily assembled gambits seemed to slow the momentum of Mr. Johnson’s political unraveling. On Wednesday, minutes before the prime minister appeared in Parliament, a Conservative lawmaker, Christian Wakeford, announced that he would join the Labour Party, delivering a stinging blow to Mr. Johnson.
Mr. Wakeford, who sat with Labour lawmakers, expressed anger at how the prime minister had handled the outcry over the parties and confirmed that he had submitted a letter calling for a no-confidence vote.
In a letter to Mr. Johnson, Mr. Wakeford said, “Both you and the Conservative Party as a whole have shown themselves incapable of providing the leadership and government this country deserves.”
Mr. Johnson’s earlier public appearances, including a television interview on Tuesday, not only failed to convince his internal critics but seemed to deepen the crisis. He showed more fight in Parliament on Wednesday, and again insisted he would not resign, but was still put on the defensive by the Labour leader, Keir Starmer, who mocked his shifting explanations about a party he attended in the Downing Street garden in May 2020.
Noting that Mr. Johnson had apologized to Queen Elizabeth II for parties held on the eve of the funeral of her husband, Prince Philip, Mr. Starmer asked, “Isn’t he ashamed he didn’t hand in his resignation at the same time?”
Mr. Johnson has struggled to sustain his argument that he did not mislead Parliament — an offense that could lead to a prime minister’s resignation — on the grounds that he thought he was attending a work event when, in May 2020, he joined several dozen staff members drinking in the garden at the height of lockdown restrictions.