A report by Britain's Open Rights Group and the LSE Media Policy Project claims that content filtering on mobile phones is being applied in a way that's both over-broad and non-transparent. Site blocking is common practice by UK mobile carriers; it's intended to prevent minors from seeing objectionable material and can be turned off by contacting the phone company. The Open Rights Group, however, says it has found several problems with the system. Blacklists can be overzealous, and getting an item removed from the list (as opposed to simply having it unblocked on a single phone) is difficult. It's also not always clear when something has been blocked or how the blacklists work. Some carriers, like O2, offer a way to check URLs against the blacklist and appeal a decision, but even these are hard to find and offer little feedback.

Any filtering system can be expected to have false positives, but the Open Rights Group says carriers aren't doing enough to address the problem. After setting up a site to collect reports on incorrectly blocked sites, the group found a number of people whose blogs or organization pages had been filtered for unclear reasons. One particularly egregious case involved a church whose site was blocked by O2 for "adult content." After reporting the error, a church member was told that he could not have the site removed from the blacklist, even though it demonstrably contained nothing "adult." In total, the team found 60 reports of incorrectly blacklisted sites in the first three months of 2012.

In order to alleviate the problem, the Open Rights Group is calling for an "active choice" model of filtering, where subscribers decide whether or not to turn on parental controls, rather than the opt-out model that's recently been proposed in Parliament. It's also asked that carriers make it easier to find and report potential errors. Without nuanced implementation, the group says, "seemingly simple, laudable goals such as protecting children through technical intervention may have significant harmful and unintended consequences for everybody’s access to information."