The co-founder of the Women’s Equality party, Catherine Mayer, is suing her former employer, Time magazine, for gender and age discrimination, making the weekly favoured by President Donald Trump the latest major media company to be embroiled in accusations of institutional sexism.

The case comes soon after publication of BBC salaries provoked outrage at both gender and race gaps in pay, and a year after a series of high-profile sexual harassment cases plunged US TV giant Fox News into turmoil.

It pits one of Britain’s most prominent journalists, who wrote a controversial biography of Prince Charles and was shortlisted for the Orwell prize, against one of America’s most famous magazines, nearly a century old and with millions of readers. Time’s brand is so powerful Trump’s golf clubs were decorated with mocked-up covers showing his face. Mayer’s suit, filed in a New York court, covers the final three years of her employment at the title, and her dismissal in 2015.

The problems began soon after she was appointed Europe regional editor, after eight years of outstanding performance and appraisals, court documents allege. The suit alleges that Time’s foreign editor appointed Matt McAllester, a younger male colleague, as her deputy, without an open selection process and in violation of promises that she could choose her team. Mayer says McAllester began a campaign to undermine and supplant her, even though she repeatedly raised complaints.

Ultimately, Mayer claims, the company took away her responsibilities as Europe editor the year after she took on the position, then forced her to relinquish the title, which the company gave to McAllester. In April 2015 she was fired.

The suit, filed on 24 July, said: “Time has violated [anti-discrimination and civil rights] laws by operating a system of male cronyism, by which men, especially former war correspondents, were favoured over women in recruitment, dismissal and promotion decisions.”

It alleges that McAllester, now editor-in-chief of Newsweek, poisoned the atmosphere in the London office so much one employee was afraid to be alone with him and eventually resigned without having another job to go to. “This was not the result of a tough but fair work regime, but from bullying some subordinates and favouring others. ‘Non-macho’ men and women who did not conform to traditional expectations of gender roles did not fare well,” the suit claims. “Staff in London quickly concluded that McAllester was trying to oust plaintiff.”

Mayer claims that when she raised concerns with the international editor, Jim Frederick, he did not provide support. “He responded simply, ‘You are two of my favourite people and I am sure you will find a way to work things out.’” Her treatment triggered serious health problems including depression, migraines and insomnia, Mayer alleges. She also claims the timing of her dismissal was particularly damaging because it coincided with publication of her controversial and high-profile biography of Prince Charles. “[It] had a negative impact on book sales and her reputation, since many assumed Time had terminated her because her research for the book was defective or for other performance-related reasons,” the suit said.

Mayer claims she contested her dismissal immediately. “There was never a point when I accepted this was a valid redundancy, and never a point when I didn’t fight back,” she said. “Of course money is relevant to this, but also they were doing me reputational damage, because of the timing of the decision.”

However, the case has come to light only after she decided to sue. Mayer said that despite her prominent position as an advocate for gender equality, she had hoped to keep her personal battle with Time quiet by reaching a private settlement. “I’m not going to try to pretend that I started out doing this for other women,” she said. “Absolutely initially what you want to do is move on with your life.”

Mayer chose to take legal action in New York, where Time and its senior management is based. She is a dual citizen of the US and Britain. After two years seeking a settlement, legal deadlines meant she had to go to court or drop her case, she said. But under the US system, that meant the suit would be public.

Mayer said that having the case made public has a silver lining. She can now discuss her personal experience, and how it forced her to confront wider problems across the profession. “If this is happening to me, what is it like to be someone less well-defended than me?” she asked.

Time did not respond to questions about the lawsuit and Mayer’s claims. Matt McAllester declined to comment.