The Open Rights Group (ORG) and the LSE Media Policy Project have published a report that lists legitimate sites that have been blocked using censorship technology.
The report's author, Open Rights Group member Peter Bradwell, warned that internet censorship on mobile networks has lead to overblocking and could cause some sites major problems if similar measures are forced upon fixed-line broadband ISP subscribers.
Bradwell's report highlights 10 examples of incorrectly blocked sites between 1st January and 31st March 2012.
He said that mobile networks in the UK are more likely to suffer from mistaken blocking than deliberate abuse.
He said that blocking extends beyond adult sexual content because it is difficult to define what is appropriate.
There are two different types of over-blocking. Sites are being misclassified and filtered. Then there are disputed classifications, where deciding what material should be considered 'blockable' requires a further - subjective - judgement.
Some networks think that forums should always be blocked, because of concerns that young people will interact with people they don't know. But this cuts off education forums and peer support sites.
The report lists a top ten of inappropriate blocks in the UK
1. Tor (www.torproject.org).
2. La Quadrature du Net (www.laquadrature.net/en). The website of this French 'digital rights' advocacy group was reported blocked on Orange's 'Safeguard' system on 2nd February.
3. Shelfappeal.com features items that can be placed on a shelf.
4. Septicisle.info which is a personal blog featuring political opinion pieces. It does not contain any adult content.
5. The Vault Bar (www.thevaultbar.co.uk) in London.
6. St Margarets Community Website (www.stmgrts.org.uk), is a community information site 'created by a group of local residents of St Margarets, Middlesex.'
7. eHow.com is an advice and educational site. It provides tutorials on a wide range of everyday issues, from 'navigating after-school care' to 'small space garden tips'.
8. Biased-BBC (www.biased-bbc.blogspot.co.uk) is a site that challenges the BBC's impartiality. It was catogorised as a hate site.
9. Yomaraugusto.com is the home page of a graphic designer, offering a portfolio of his art and design work.
10. Equisitetweets.com allows users to create one-page threads to save or share from conversations on Twitter.
Clearly threatening stuff, then.
The report said that UK network operators fail to provide a clear path for appealing unfair blocks. This is a nightmare if you are a legitimate business - such as clothes and underwear retailers Bravissimo and Figleaves who were blocked.
The report calls for the government to "reject 'default on' network filtering" in its new consultation and instead suggests that they should "work to give parents simpler choices and better, device-based tools".