Frances Haugen, the Facebook whistle-blower, testifies in Parliament.

British policymakers heard testimony on Monday from the former Facebook manager who became a whistle-blower and shared scores of internal documents with policymakers, regulators and journalists to help build a case for stiffer oversight of the social media giant.

Frances Haugen, the former employee, spoke before a Parliament committee as part of her tightly choreographed campaign to reveal internal Facebook research and discussions that paint a portrait of a company vividly aware of its harmful effects on society, contrary to public statements by company leaders.

Here are some highlights from the session:

• In the opening moments of her testimony, Ms. Haugen likened Facebook to an “oil spill” and said government officials must act quickly to avoid more damage. “I came forward because now is the time to act,” she said.

• Ms. Haugen said more transparency is needed from Facebook, which she said presented a false picture of its efforts to delete hate speech and other extreme content. The company says artificial intelligence software catches more than 90 percent of hate speech, but Ms. Haugen said the number was less than 5 percent.

  “They are very good at dancing with data,” she said.

• Ms. Haugen urged policymakers to reduce Facebook’s use of “engagement-based rankings,” the process by which its algorithm amplifies some content more than others based on how much other Facebook users interact with it through “likes,” shares and other metrics.

  Such a system, Ms. Haugen said, prioritizes and amplifies polarizing and extreme content. “Anger and hate is the easiest way to grow on Facebook,” she said.

• Facebook puts “growth over safety,” Ms. Haugen said, particularly in areas of Africa, Asia and the Middle East where the company does not have language or cultural expertise and where the platform has exaggerated divisions among users.

  She said events in countries such as Ethiopia and Myanmar, where Facebook has been accused of contributing to ethnic violence, were the “opening chapters of a novel that is going to be horrific to read.”

• John Nicolson, a member of the committee from Scotland, described receiving homophobic abuse online. He said it was just one example of the problems caused by social media. He cited an internal study from Facebook revealed by Ms. Haugen that found that 13 percent of surveyed British teenagers connected a desire to commit suicide to Instagram.

  He asked: “Is Facebook evil?”

  “I cannot see into the hearts of men,” Ms. Haugen responded.

Even for Facebook, a company that has lurched between controversies since Mark Zuckerberg started it as a Harvard undergrad in 2004, Ms. Haugen’s disclosures have created a backlash and public relations crisis that stands apart. It has put the company on the defensive, helping attract political support for new regulation in the United States and Europe and leading to some calls for Mr. Zuckerberg to step aside as Facebook’s chief executive.

The testimony in Britain on Monday is part of the next phase ofMs. Haugen’s campaign against Facebook, a company that she says has put “profit over people.” After anonymously leaking internal Facebook research to The Wall Street Journal that resulted in a series of articles that began in September, she revealed her identify early this month for an episode on “60 Minutes” and testimony before a Senate committee. The documents, which include slide decks, internal discussion threads, charts, memos and presentations, have also been shared with the Securities and Exchange Commission.

Since then, she has shared the Facebook materials with other news organizations, including The New York Times, resulting in additional stories about Facebook’s harmful effects, including its role in spreading election misinformation in the U.S. and stoking divisions in countries such as India.

Ms. Haugen is now making a tour across Europe, home to some of the world’s most aggressive tech regulation and where governments are expected to act faster than the United States to pass new laws targeting Facebook and other tech giants. After testifying before British lawmakers, Ms. Haugen is scheduled to meet in the coming weeks with officials in Brussels, Paris and Berlin. She is also scheduled to speak at an industry conference in Lisbon.

“For all the problems Frances Haugen is trying to solve, Europe is the place to be,” said Mathias Vermeulen, the public policy director at AWO, a law firm and policy firm that is among the groups working with Ms. Haugen in the United States and Europe.

British policymakers are hearing Ms. Haugen’s testimony as they draft a law to create a new internet regulator that could impose billions of dollars worth of fines if more isn’t done to stop the spread of hate speech, misinformation, racist abuse and harmful content targeting children.

The policy ideas gained additional momentum after the murder this month of David Amess, a member of Parliament, leading to calls for the law to force social media companies to crack down on extremism.

Later this week, representatives from Facebook, Google, YouTube, Twitter and TikTok are scheduled to testify before the same British committee as will Ms. Haugen.

In Brussels, Ms. Haugen is scheduled to meet on Nov. 8 with European Union officials draftinglaws that would force Facebook and other large internet platforms to disclose more about how their recommendation algorithms choose to promote certain material over others, and impose tougher antitrust rules to prevent the companies from using their dominant positions to box out smaller rivals. European policymakers are also debating a ban on targeted advertising based on a person’s data profile, which would pose a grave threat to Facebook’s multibillion-dollar advertising business.

Despite growing political support for new regulation, many questions remain about how such policies would work in practice.

Regulating Facebook is particularly complex because many of its biggest problems center on content posted by users all over the world, raising difficult questions about the regulation of speech and free expression. In Britain, the new online safety law has been criticized by some civil society groups as being overly restrictive and a threat to free speech online.

Another challenge is how to enforce the new rules, particularly at a time when many government agencies are under pressure to tighten spending.