More officials resign, including a minister who defended Johnson two days earlier.

LONDON — Britain’s minister for children and families resigned on Wednesday morning, becoming the latest in a growing exodus of officials from the scandal-engulfed government of Prime Minister Boris Johnson. Only two days earlier, the minister, Will Quince, had stoutly defended Mr. Johnson’s role in the promotion of a Conservative lawmaker accused of sexual misconduct and excessive drinking.

“With great sadness and regret, I have this morning tendered my resignation to the Prime Minister after I accepted and repeated assurances on Monday to the media which have now been found to be inaccurate,” Mr. Quince said on Twitter.

Mr. Quince’s case laid bare one of Mr. Johnson’s vulnerabilities in this season of scandal: Not only has the prime minister been accused of dissembling and issuing false statements, but Downing Street has also sent out representatives to television news studios to repeat those erroneous claims on behalf of Mr. Johnson.

In his statement, Mr. Quince said Downing Street had given him a “categorical assurance” that Mr. Johnson had not been aware of any “specific” allegation against the Conservative lawmaker, Chris Pincher, before appointing him to the post of the party’s deputy chief whip this year. Downing Street later admitted that was not true.

Robin Walker, the minister of state for school standards, also stepped down on Wednesday, citing Mr. Johnson’s increasingly tumultuous tenure, including the resignation of Rishi Sunak as chancellor of the Exchequer and Sajid Javid as health secretary.

“Unfortunately,” Mr. Walker wrote in a letter that he then posted on Twitter, “recent events have made it clear to me that our great party, for which I have campaigned all of my adult life, has become distracted from its core missions by a relentless focus on questions over leadership.”

Mr. Walker added that the loss of Mr. Sunak and Mr. Javid — whom he described as “two of our broadest talents” —  reflected “a worrying narrowing of the broad church that I believe any Conservative government should seek to achieve.”

Addressing Mr. Johnson in the letter, Mr. Walker wrote: “You won the confidence of your colleagues just a few weeks ago, but the events and revelations since have undermined this. I have publicly supported you as leader of our party and prime minister, but I am afraid I feel I can do so no longer.”