Treasury chief Rishi Sunak and Health Secretary Sajid Javid resigned within minutes of each other.
“I can no longer continue in good conscience,” Javid said.
Johnson has been hit by allegations he failed to come clean about a lawmaker who was appointed to a senior position despite claims of sexual misconduct.
“The public rightly expect government to be conducted properly, competently and seriously,” Sunak said.
“I recognise this may be my last ministerial job, but I believe these standards are worth fighting for and that is why I am resigning.”
Earlier on Tuesday (UK time), a former top British civil servant said Boris Johnson’s office wasn’t telling the truth about sexual misconduct allegations against lawmaker Chris Pincher, who resigned as deputy chief whip on Thursday amid complaints he groped two men at a private club.
The government’s explanation shifted repeatedly over the past five days. Ministers initially said Johnson was not aware of any allegations when he promoted Pincher to the post in February.
On Monday, a spokesman said Johnson knew of sexual misconduct allegations that were “either resolved or did not progress to a formal complaint”.
That account did not sit well with Simon McDonald, the most senior civil servant at the UK Foreign Office from 2015 to 2020. In a highly unusual move, he said on Tuesday that the prime minister’s office still wasn’t telling the truth.
McDonald said in a letter to the parliamentary commissioner for standards that he received complaints about Pincher’s behaviour in the summer of 2019, shortly after Pincher became a Foreign Office minister. An investigation upheld the complaint, and Pincher apologised for his actions, McDonald said.
McDonald disputed that Johnson was unaware of the allegations or that the complaints were dismissed because they had been resolved or not made formally.
“The original No. 10 line is not true, and the modification is still not accurate,” McDonald wrote, referring to the prime minister’s Downing Street office.
“Mr Johnson was briefed in person about the initiation and outcome of the investigation.
“There was a ‘formal complaint’. Allegations were ‘resolved’ only in the sense that the investigation was completed; Mr Pincher was not exonerated.
“To characterise the allegations as ‘unsubstantiated’ is therefore wrong.”
Hours after McDonald’s comments came out, Johnson’s office changed its story again, saying the prime minister forgot he was told that Pincher was the subject of an official complaint.
The office confirmed Johnson was briefed on the complaint by Foreign Office officials in 2019, a “number of months” after it took place. His office said it took some time to establish the briefing took place.
Cabinet Office minister Michael Ellis told lawmakers in the House of Commons that when Johnson was made aware of the issue in late 2019, he was told that the permanent secretary had taken the necessary action and so there was no question about Pincher remaining as a minister.
“Last week, when fresh allegations arose, the prime minister did not immediately recall the conversation in late 2019 about this incident,” Ellis said.
“As soon as he was reminded, the No. 10 press office corrected their public lines.”
The latest revelations are fuelling discontent within Johnson’s cabinet after ministers were forced to publicly deliver the prime minister’s denials, only to have the explanation shift the next day.
Two weeks later, Conservative candidates were badly beaten in two special elections to fill vacant seats in Parliament, adding to the discontent within Johnson’s party.
When Pincher resigned last week as deputy chief whip, a key position in enforcing party discipline, he told the prime minister he “drank far too much” and had “embarrassed myself and other people”.
Johnson initially refused to suspend Pincher from the Conservative Party, but he relented after a formal complaint about the groping allegations was filed with parliamentary authorities.
Critics suggested Johnson was slow to react because he didn’t want to be in the position of forcing Pincher to resign his Parliament seat and setting up the Conservatives for another potential special election defeat.
Even before the Pincher scandal, suggestions were swirling that Johnson may soon face another no-confidence vote.
In the next few weeks, Conservative lawmakers will elect new members to the committee that sets parliamentary rules for the party. Several candidates have suggested they would support changing the rules to allow for another vote of no confidence. The existing rules require 12 months between such votes.
Senior Conservative lawmaker Roger Gale, a long-standing critic of Johnson, said he would support a change of the rules of the Conservative 1922 Committee.
“Mr Johnson has for three days now been sending ministers — in one case a Cabinet minister — out to defend the indefensible, effectively to lie on his behalf. That cannot be allowed to continue,” Gale told the BBC.
“This prime minister has trashed the reputation of a proud and honourable party for honesty and decency, and that is not acceptable.”