When British Prime Minister David Cameron fought last year to place content filters on British Internet service providers (ISPs) in the U.K., he said it it was intended to prevent children from being exposed to pornography.

But now, it appears these filters are doing a whole lot more than just blocking pornography. Brits are being blocked from accessing political blogs, medical information pages and whole host of other innocuous websites.

In fact, a full one-fifth of the 100,000 most popular webpages are being blocked by British ISP filters, reports the Open Rights Group (ORG), an Internet watchdog organization. They say the filters are so restrictive that websites that were previously only blocked in repressive countries like China and Russia are now being blocked in the U.K.

ORG created a free Web tool for people to see which websites are blocked by which IPS filters. Using this tool on their own,ORG found that some 19,000 sites are blocked by at least one filter.

“Through the Blocked project we wanted to find out about the impact of web filters," Jim Killock, ORG's executive director, said in a statement. "Already, our reports are showing that almost one in five websites tested are blocked, and that the problem of overblocking seems much bigger than we thought."

It's currently unclear why certain harmless websites are being blocked by filters designed to prevent British young people from viewing hardcore pornography. There is little transparency about how the Web filters actually work, but one might assume that ISPs have been overzealous in crafting their filters to stay on the right side of the new law—a pet initiative of the prime minister.

British citizens, bloggers and businesses say the filters have been a hindrance to their online activities. The editor of the feminist site She Rights says the number of visitors to her site has plummeted since her blog was blocked by one of the filters. Paul Staines, editor of the political blog Guido Fawkes, says he's also been blocked by the filter of ISP TalkTalk.

"We would really appreciate it if TalkTalk would remove us from their block list," Staines said. "The only people who block us are them and the Chinese government."

ORG also relays the story of a mother who said she was "humiliated" by the process of trying to circumvent a filter to access a page on postpartum care.

When contacted by Motherboard, a spokesperson for TalkTalk said that the ISP had "been testing on a slightly higher default setting," with their filter and noted that the filter might not be right for everybody right now.

This isn't the first report of the filter blocking unintended sites. In January, outlets reported that the ISP filters were blocking access to the game League of Legends

Since their implementation last year, ISP filters have been widely criticized by many free speech advocates and porn industry officials who have labeled the policy censorship.

H/T: Motherboard | Photo by U.K. Department for International Development/Flickr (CC BY 2.0)