This January, under government pressure, many of the United Kingdom’s internet service providers (ISPs) — together providing over 90 percent of the country’s home broadband connections — turned on “porn filters” for all of their customers, requiring them to actively turn off the filters to view any content deemed unsuitable. Prime Minister David Cameron pushed the program through under the guise of protecting the “innocence of children,” but as warned by opponents of Internet regulation, the filters are now blocking large amounts of clean content. To show just how restrictive these web blockers are, the nonprofit Open Rights Group recently released an online tool to let anyone see how many of the UK’s ISPs block a given website. ORG also tested the 100,000 most-visited domains and found nearly 20 percent were blocked by at least one service provider, including numerous sites that were perfectly innocent.

Already alarmed that UK residents couldn’t access a fifth of the Internet unless they made an embarrassing call requesting their ISP to unblock adult content, I wanted to see exactly what the filters were blocking. My first thought was to check the site for Students for Sensible Drug Policy, an international grassroots advocacy organization for which I chair the board of directors. Expecting our political website to easily avoid filters intended to block obscenity, I almost didn’t believe it when the tool showed it was blocked by four ISPs.

Discovering that citizens of a supposedly free country were being denied access to SSDP’s website was infuriating. While being targeted for our political beliefs by institutions from the IRS to public universities to Chase Bank is nothing new, surging poll numbers and supportive statements from Bill Clinton and other members of the political establishment had made it seem like those days might be behind us.

To make sure SSDP being blocked wasn’t a fluke, I ran the websites for eight other leading U.S. and UK drug policy reform organizations through ORG’s tool. All but one were blocked by at least one ISP, and most by many more:

This reinforced my suspicion that the government-backed filters could be systematically restricting content criticizing the War on Drugs. Yet while all advocate for drug policy reform, not drug use, it was possible the mere mention of words like “marijuana” or “drugs” was enough to set off the filters. If that were the case, they’d also be blocking websites opposing marijuana regulation and other reforms, since they mention those keywords just as frequently.

To see if this was happening, I tested nine organizations supportive of the Drug War, from nonprofits to government entities. This had very different results, with most sites passing every single filter, and only two getting caught in any:

Internet filters pushed for by the UK government are only letting through one side of the global discussion on drug policy, and it just so happens to be the status quo. This not only prevents education, as when UK residents are unable to read this SSDP blog post on their government clinging to the Drug War and firing people like David Nutt who question their approach. It also hamstrings action: students prevented from accessing SSDP’s website not only can’t learn about our mission, they can’t find out how to start a chapter on their own campus. They’re similarly blocked from signing petitions hosted by these nonprofits or even donating money to help them operate.

There is still some hope that these lopsided restrictions are an accident. But intentional or not, this censorship is real, and is actively restricting the political education and activities of UK residents. The ISPs involved need to unblock these and other non-obscene sites immediately, and defenders of the open Internet should remember this whenever reactionaries in their countries try to block large swaths of the Web under whatever pretense is popular at the time.

CORRECTION: A previous version of this post stated that Virgin Media, which tied for blocking the most reform organizations in the sample, is owned by drug reform activist Richard Branson. Branson was a part owner until Liberty Global acquired the company in 2013.