The unreliability of internet filters has been demonstrated at the British Library, where its WiFi network blocked an author from reading an online version of Shakespeare's Hamlet, as it was deemed to contain "violent content".
Author Mark Forsyth was writing a book in the library and needed to check a line from the famous play, reports the BBC.
The British Library told the BBC the problem was caused by a newly installed WiFi service from a third-party provider that contained internet filters.
Prime minister David Cameron's plan to force ISPs to turn on internet filters "by default" to stop "adult content" for new customers have been criticised in some quarters.
Cameron's stance is that such filters make it harder for children to view adult content, although they could inadvertently block other content which isn't necessarily targeted by the government.
Wikipedia co-founder Jimmy Wales, a key technology adviser to prime minister David Cameron, slammed the government's demand that ISPs should introduce porn filters by default, saying the move is "ridiculous".
While ISP filters in people's homes can be turned off, that isn't the case for users of services in places like the British Library.
One security expert told the BBC the British Library incident highlighted the "dysfunction" of internet filters.
Professor Ross Anderson, a security expert at Cambridge University, said that internet filters were "pointless" and that it was "completely inappropriate" to have one in the British Library.
Anderson said: "Everything that is legal should be available over the library's WiFi network. The only things they should block are the few dozen books against which there are court judgements in the UK.
"One of the functions of deposit libraries is to keep everything, including smut."
A spokesperson for the British Library told the BBC that Hamlet had since been made accessible. They said the filters were aimed at protecting children visiting the building from content "such as pornography and gambling websites".