LONDON — Prime Minister Truss described herself as “a fighter and not a quitter” Wednesday as she faced down a hostile opposition and fury from her own Conservative Party over her botched economic plan.

Yet within hours of Ms. Truss’ appearance at the weekly Prime Minister’s Questions session, a senior member of her government left her post with a fusillade of criticism, and a House of Commons vote descended into acrimony and accusations of bullying.

The Home secretary, Suella Braverman, said she resigned after breaching rules by sending an official document from her personal email account. 

In her resignation letter, Ms. Braverman said she had “concerns about the direction of this government” and — in a thinly veiled attack on Ms. Truss — said “the business of government relies upon people accepting responsibility for their mistakes.”

“Pretending we have’’t made mistakes, carrying on as if everyone can’t see that we have made them and hoping that things will magically come right is not serious politics,” she said.

Ms. Braverman is a popular figure on the Conservative Party’s right wing and a champion of more restrictive immigration policies. She ran unsuccessfully for Conservative Party leader this summer, a contest won by Ms. Truss.

Ms. Braverman was replaced as home secretary, the minister responsible for immigration and law and order, by a former Cabinet minister, Grant Shapps. He’s a high-profile supporter of the former Treasury chief, Rishi Sunak, who Ms. Truss defeated in the final round of the Conservative leadership race.

Ms. Truss faced another test in Parliament on Wednesday on a vote over fracking for shale gas — a practice that Ms. Truss wants to resume, despite opposition from many Conservatives.

With a large Conservative majority in Parliament, an opposition call for a fracking ban was easily defeated by 326 votes to 230, but some lawmakers were furious that Conservative Party whips said the vote would be treated as “a confidence motion in the government,” meaning the government would fall if the motion passed.

There were angry scenes in the House of Commons during and after the vote, with party whips accused of using heavy-handed tactics to gain votes. Labor lawmaker Chris Bryant said he “saw members being physically manhandled … and being bullied.” 

There were unconfirmed reports that the Conservative chief whip, Wendy Morton, who is responsible for party discipline, had resigned.

Conservative lawmaker Charles Walker said it was “an embarrassment and a disgrace.”

The dramatic developments came days after Ms. Truss fired her Treasury chief, Kwasi Kwarteng, on Friday after the pro-growth, supply-side economic package the pair unveiled September 23 spooked financial markets and triggered an economic and political crisis.

The plan’s 45 billion pounds, or $50 billion, in unfunded tax cuts sparked turmoil on financial markets, hammering the value of the pound and increasing the cost of U.K. government borrowing. The Bank of England was forced to intervene to prevent the crisis from spreading to the wider economy and putting pension funds at risk.

On Monday Mr. Kwarteng’s replacement as Treasury chief, Jeremy Hunt, scrapped almost all of Ms. Truss’ tax cuts, along with her flagship energy policy and her promise of no public spending cuts. 

Mr. Hunt said the government will need to save billions of pounds and there are “many difficult decisions” to be made before he sets out a medium-term fiscal plan on October 31.

Speaking to lawmakers for the first time since the U-turn, Ms. Truss apologized Wednesday and admitted she had made mistakes, but said that by changing course she had “taken responsibility and made the right decisions in the interest of the country’s economic stability.”

Opposition lawmakers shouted “Resign!” as she spoke.

Asked by the opposition Labor Party leader, Sir Keir Starmer, “Why is she still here?” Ms. Truss retorted: “I am a fighter and not a quitter. I have acted in the national interest to make sure that we have economic stability.”

Official figures released Wednesday showed U.K. inflation rose to 10.1 percent in September, returning to a 40-year high first hit in July, as the soaring cost of food squeezed household budgets. 

While inflation is high around the world — driven up by Russia’s invasion of Ukraine and its effect on energy supplies — polls show most Britons blame the government for the country’s economic pain.

Opponents also accuse the Conservative government of sowing chaos by flip-flopping on policy. On Wednesday, Ms. Truss reassured retirees that pensions would continue to rise in line with inflation — less than 24 hours after her spokesman said the government was considering removing the expensive pledge as it seeks to cut public spending.

With opinion polls giving the Labor Party a large and growing lead, many Conservatives now believe their only hope of avoiding electoral oblivion is to replace Ms. Truss. Yet she says she is not stepping down, and legislators are divided about how to get rid of her.

A national election does not have to be held until 2024. Ms. Truss appeared to rule out calling an early election, saying Wednesday that “what is important is we work together … to get through this winter and protect the economy.”

Under Conservative Party rules, Ms. Truss technically is safe from a leadership challenge for a year, but the rules can be changed if enough lawmakers want it. There is fevered speculation about how many lawmakers have already submitted letters calling for a no-confidence vote, and tensions rose further on Wednesday evening.

As yet, there is no front-runner to succeed her. Mr. Sunak, the House of Commons leader, Penny Mordaunt, and the popular Defense secretary, Ben Wallace, all have supporters, as does Mr. Hunt, whom many see as the de facto prime minister already.

Some even favor the return of Prime Minister Johnson, who was ousted in the summer after becoming enmeshed in ethics scandals.