Members of the No More Page 3 campaign hit the streets of London protesting the 43-year practice of displaying nude female models in the pages of the British newspaper, The Sun. (Karla Adam/The Washington Post)

Britain’s best-selling Sun newspaper has called the photos of topless women famously featured on Page 3 a “British institution” — on par, seemingly, with a full English breakfast or queueing quietly at bus stops.

But for a new wave of feminists as tenacious as they are Twitter savvy, the Sun’s daily dose of bare breasts is not a quirky tradition worth celebrating but a poignant example of modern-day sexism.

The plainly named “No More Page 3” campaign has become one of the highest-profile of many recent feminist efforts in Britain that are fueled by social media and other online tools.

For its part, the Sun is characteristically unrepentant over its signature pictures.

In an interview with the BBC last month, Sun Editor David Dinsmore said that the paper polled focus groups and that “the result comes back a resounding, ‘Keep it there! Don’t take it away!’ ” He added, “I’m making a paper for the readers.”

When asked what Page 3 brings to readers, Dinsmore said, “A smile.”

Apparently, though, not to everyone.

The campaign’s founder, Lucy-Anne Holmes, remembers reading the newspaper as a girl and anxiously comparing her body with those of the topless models staring back at her. “I was comparing my breasts to these girls, and I just assumed at age 11 my breasts were there for men to see, which is a powerful thing,” Holmes said.

She launched the campaign last year after noticing that during the London Olympics, the most prominent image of a female in the newspaper wasn’t an athlete but a topless model.

Meanwhile, the Page 3 models are still there, but the campaign is making strides.

In August, the Irish edition of the Sun ditched its photos of topless models, citing “cultural differences” between Ireland and Britain. Dozens of universities have yanked copies from their shelves. Nearly 130,000 people — including 150 members of Parliament — have signed an online petition asking the editor to drop the feature. The group Girlguiding has voiced its support, as have teachers unions and the Welsh government.

So what? supporters say. It’s a bit of harmless fun, they say, and if you don’t like it, don’t buy it. Besides, the argument goes, we live in an era in which Miley Cyrus casually tweets pictures of herself (nearly) topless to millions of followers and much raunchier images are only a click away.

This isn’t the first concerted stand against Page 3, which has long been a lightning rod for feminists. In 1986, Clare Short, then a Labor Party member of Parliament, introduced a bill in the House of Commons to remove such images from the newspaper. Illustrating its propensity to attack those who attack it, the paper responded by calling her “fat” and “jealous.”

The photos remained. Then, in 2004, after Short told a female reporter that she still found the images pornographic, the attacks resumed, including a double-decker bus filled with Page 3 models parked outside her home in London.

In a sign of how visible the campaign has become, British Prime Minister David Cameron has been asked about it repeatedly, including last week in Parliament. He said that it’s up to consumers to decide whether to buy the paper and that he does not support a ban on the images.

Campaigners say they aren’t asking for legislation and just want the paper to drop the images, which they say objectify and demean women and, unlike pornography, are easily seen by children.

The Sun introduced topless models in 1970, under the helm of its new owner, Rupert Murdoch. A year later, circulation had shot up 29 percent.

The feature has changed over the years. There are no more topless models on the weekend, no more girls younger than 18, no more surgically enhanced breasts, no more “News in Briefs,” a box next to the model with pithy comments on the news of the day.

But there is a growing sense that the images are a leftover vestige of a bygone era, a time of scantily clad women chasing Benny Hill. Even Murdoch tweeted in February that he was considering whether the images were “so last century.”

The campaign against Page 3 is part of a larger resurgence of feminist activism in Britain, with many women, like Holmes, using social media and personal stories to propel causes.

For instance, one of the most wildly popular recent efforts is the Everyday Sexism Project, a Web site and Twitter account that catalogue stories of daily harassment. It has spread to 18 countries since its launch last year.

“So many voices are speaking up at the same time,” said Laura Bates, 27, who founded the project after a stranger groped her on the street in London. “It’s giving people the strength and confidence to talk about it,”

Kira Cochrane, author of “All the Rebel Women,” which chronicles Britain’s “fourth wave” of feminism, said that “this resurgence feels like something different — technological tools have moved on, and you have tools that allow 150,000 people to get involved at quite a low level. The level of engagement is in­cred­ibly high.”

In the case of the Sun, which did not return calls from a reporter, the topless models are still there, one flick away from the front page, evoking emotions on both sides of the debate.

“I love Page 3!” a bespectacled man recently yelled from a yellow van as he tooted his horn and sped past a group of anti-Page 3 protesters marching in central London.

Emily Wearmouth, a 32-year-old Londoner who was in the march with her mother and infant son, said, “It’s really important that our major, most widespread national newspaper treats women in a more respectful manner, rather than objectifying us over everybody’s breakfast.”