LONDON — As swirling allegations of sexual harassment and inappropriate behavior engulf British politics, the country’s defense secretary, Michael Fallon, has quit, and others are under pressure to do the same.

But the choice of Gavin Williamson as Mr. Fallon’s replacement also caused a stir, upsetting fellow Conservatives who thought his promotion to the cabinet from the job of chief whip, responsible for party discipline, was premature. And, in an unusual twist, the ambitious Mr. Williamson is perhaps best known for keeping a pet tarantula at his desk.

In Britain, politics sometimes seems to resemble an implausible plotline from “House of Cards,” the long-running drama about a chief whip who schemes his way to power, which originated here. Production was suspended on the American version of the series after its star, Kevin Spacey, was accused of making a sexual advance on a 14-year-old boy.

On Thursday, Prime Minister Theresa May was hoping to contain the damage from a broad array of misconduct claims centered on her Conservative Party, ranging from sexual assault to casual sexism to extramarital affairs.