Politicians now wonder whether a tipping point has been reached, one that will force lawmakers and officials to clean up their act as they did after a scandal broke in 2009 over inflated expense claims.
On Wednesday night, the leader of the Scottish Conservatives, Ruth Davidson, likened British politics to the mythical Augean stables with, she said, some “pretty big shovels” needed for the clean up.
“The dam has broken on this now, and these male-dominated professions, overwhelmingly male-dominated professions, where the boys’ own locker room culture has prevailed and it’s all been a bit of a laugh, has got to stop,” she later told the BBC.
For the embattled Mrs. May, already presiding over a weakened and divided government fighting over plans for the British withdrawal from the European Union, the scandal is an unwanted distraction.
Mr. Williamson’s appointment, made in a brief statement by Mrs. May’s office on Thursday morning, suggested that she wanted to keep changes to her top team as minimal and low key as possible for now.
But in a surreal coda to the mini-reshuffle, the new chief whip, Julian Smith, who replaced Mr. Williamson, marked his promotion by tweeting a picture of the pet tarantula that had been kept by his predecessor.
The rapid rise of Mr. Williamson, who has not run a government department, provoked criticism from some Conservative lawmakers, including Sarah Wollaston, who argued that others may have been better qualified.
But probably a bigger danger to Mrs. May is the risk of further resignations that could expose the government to more bad publicity, and potentially disrupt the political balance of the cabinet.
In Mr. Fallon’s case the immediate allegations centered on an incident in which he put his hand on the knee of a female journalist, Julia Hartley-Brewer, at a dinner.
When the account broke it looked unlikely to prompt a cabinet resignation, partly because it dated from 2002, partly because Ms. Hartley-Brewer made light of the episode and partly because Mrs. May’s office, initially, did not consider an investigation necessary.
But on Wednesday night all that changed, leading to speculation that Mr. Fallon quit because he could not assure Mrs. May that there were no further embarrassments to come.
“The culture has changed over the years,” Mr. Fallon told the BBC, when asked whether he feared more such news might emerge. “What might have been acceptable 15, 10 years ago is clearly not acceptable now. Parliament now has to look at itself.”
In the short term that involves examining the conduct of at least two other ministers.
The Cabinet Office is investigating one of them, Mark Garnier, an international trade minister, who has admitted that before he took up his ministerial post, he had asked a female member of his staff to buy sex toys.
The other, Damian Green, a senior cabinet minister and one of Mrs. May’s closest allies, has described as completely false allegations that he behaved inappropriately toward a female activist.
More than 30 Conservative lawmakers have been mentioned on a poorly vetted list circulating on social media that is nothing more than hearsay. That has prompted furious denials from two prominent lawmakers whose names appear on the list, Rory Stewart and Dominic Raab.
Other claims have involved the opposition Labour Party, and even government critics concede that the problems are not confined to its ranks.
Indeed the most serious public allegation so far came from a Labour activist, Bex Bailey, who told the BBC earlier this week that she suffered a serious sexual assault at a Labour event in 2011 and that, when she later asked for advice from a senior staff member, she was told that formally reporting what had occurred could damage her career prospects.
Mrs. May is hoping to meet other party leaders on Monday to discuss new steps to ensure that Westminster is a secure environment for its workers, and that those who suffer harassment can make complaints in confidence.
Some changes are likely, and the crisis may mean the end to a system under which lawmakers employ their parliamentary staff directly, something that makes it hard to report abuse.
But the scandal has raised a whole series of questions, partly because Mr. Fallon is assumed to have resigned not for what has emerged, but for other embarrassments that have yet to surface.
In addition, he has not given up his seat as a lawmaker, suggesting that some forms of behavior remain acceptable for backbenchers in Parliament but not for ministers.
In the short term, the crisis may play to one of Mrs. May’s strengths: she has always stood aloof from the clublike aspects of life in Parliament.
When Mrs. May ran for the leadership of her party last year one of her pitches was that she did not “gossip about people over lunch” or “go drinking in Parliament’s bars.”
Not all of her possible rivals for the leadership have the same reputation, including Foreign Secretary Boris Johnson, who has led a more colorful private life.
Asked on Thursday whether his behavior had always been up to the standards expected of a cabinet minister, Mr. Johnson replied, “You bet.”
May Names New UK Defense Secretary as Harassment Scandal Widens – New York Times