The British prime minister thinks he can stop people watching pornography. Tech experts doubt it. But one thing is certain: his anti-porn crusade has kicked up a hornet’s nest.

David Cameron’s initiative to cut off his nation’s porn supply was met with a barrage of anger, consternation, and ridicule when announced on Monday. According to the new rules, adult content will be automatically blocked from every home computer in Britain unless it is specifically requested by the Internet account holder. And that could spark a lot of awkward conversations between spouses, roommates, and teenage boys and their mothers.

Cameron’s sweeping alterations also include a deal with Britain’s biggest wifi providers and mobile phone companies to block content deemed inappropriate for under-18s for anyone in a public place.

The new rules stunned industry insiders who thought a less far-reaching compromise deal had been struck. “Something’s obviously gone wrong,” Dominique Lazanski, a former employee at Yahoo! and Apple, told the Daily Beast. “It’s very strange, they’ve been working on this deal for two years and then, between the negotiating table and Number 10, something changed.”

Internet security analysts said the move would do little to sanitize the darkest corners of the Internet and instead enrage regular Internet users who are likely to be blocked from thousands of perfectly safe websites by blunt-edged filters. All Internet account holders will be asked in the coming year if they want to remove new filters that would apply to every device in the household. But tech experts say the filters will be easy to evade, using VPN or proxy servers.

“It’s impossible for a politician to be successful in blocking porn online,” said Lazanski. “There seems to have been a lack of understanding at No. 10.”

The severity of the filters will be dictated by the service providers, although an independent watchdog will ensure they are sufficiently rigorous.

Civil liberties campaigners complained the prime minister had conflated two separate issues. As well as restricting access to legal pornography, Cameron on Monday promised to make it illegal to download some forms of extreme pornography, including simulated rape scenes, and force search engines, like Google, to block search terms that relate to child abuse footage. If users do access abuse images, a pop-up window will warn them not to proceed.

Cameron’s personal quest to clean up the Internet intensified after he met the parents of two children who were killed by pedophiles, both of whom had accessed child abuse images online. “There is no single silver bullet, there is no single solution but I think I’ll be able to look those parents in the eye and say we’re doing everything we possibly can to help make this situation better,” he told Channel 5.

The worst of these extreme images are not typically found by regular browsing or by using traditional search engines, however, but shared peer-to-peer by pornography rings or accessed via anonymous networks.

Jim Gamble, the former head of the Child Exploitation and Online Protection agency, said the proposals will be ineffective against the worst of the images. “Let’s create a real deterrent. Not a pop-up that pedophiles will laugh at but an actual deterrent where we see pedophiles being led from the police car to the court room,” he told the BBC.

The new rules are more likely to prevent people from finding information on breast cancer, sex education or wine-tasting, which have been classified as suitable for over-18s in the U.K., civil liberties advocates say.

Jim Killock, from the Open Rights Group, said Cameron’s plan was not only bound to fail but also sets a dangerous precedent of government intervention when it comes to freedom of expression and access to information. “I’m not sure censorship is ever the answer,” he said. “It’s a shocking attempt to claim the moral high ground… I don’t think he fully understands what he is proposing.”

A Member of Parliament for the Liberal Democrats, which is part of the coalition government, agreed that Cameron had struggled to accurately describe his own policy. “His rhetoric is not quite how things will be,” Julian Huppert told the Daily Beast. “I think he’s slightly exaggerating the point.”

Huppert said he, too, had grave concerns about the affect of implementing widespread filters. “Too often they over-block—for instance for young people unsure about their sexuality—if you filter out references to homosexuality, then you make things a lot worse for children. It’s very hard to get filtering correct.”

The Daily Mail newspaper, which had led a charge to crack down on “filth” online, may inadvertently get caught by the filter, too, because of the newspaper’s frequent use of photos of women in swimwear on its online site.

While Cameron’s anti-porn initiative may win favor in some conservative circles, it is unlikely to secure widespread support. “The fact is people like pornography,” said Alan Thomson, a London website designer. “Forcing people to explain to their mother, wife, or roommate why they want the porn filter off is hardly going to be a vote winner.”