Block this.

David Cameron is today expected to announce measures cooked up with the help of Christian advocacy group Mother’s Union and supported by the Big Four ISPs (BT, Virgin, TalkTalk, Orange) that will see what is loosely termed “pornography” turned into an opt-in affair. That is, if you’re a subscriber to one of those ISPs (and most people are), you won’t by default by able to look at anything deemed pornographic by the filtering system.

There are more than a few snags (as well as some worrying trends) going on here.

The first issue is that of simple effectiveness. Anybody who uses a mobile phone to access the Internet will have run into a similar opt-in system employed by the mobile telecoms operators, a system most notable for having that winning combination of properties — trivial to evade if you’re adept (like most teenagers), woefully bad at actually blocking pornography, littered with false positives (I’ve even seen reports of the BBC News website being blocked as “adult content”), and an utter pain to get switched off. Rather than being any kind of effective “adult content filter”, the system has rapidly become just another hoop people jump through. The mobile Internet system is being touted as evidence that such a system can work and is being used as the model to follow.

The biggest danger is that people — particularly parents, noting that this is a scheme intended to “protect” children — will actually think it’s an effective porn-blocking system, when it’s actually nothing of the sort. Uninformed parent (and most will be, given this scheme will no doubt be turned into a selling point by the ISPs implementing it) leaves Little Johnny to play on the Internet to his heart’s content, safe and secure in the knowledge that the magical filters will protect him from anything inappropriate. The inner workings of the Internet are sufficiently indistinguishable from magic to most people that it will just work is a perfectly reasonable belief to hold.

What happens when partner of uninformed parent as, unbeknownst to them, requested the filter be disabled because it stopped them from getting to their favourite sites (pornographic or otherwise)? Incensed that the system allowed Little Johnny to peruse some of the Internet’s more titillating corners? An enraged phonecall to the ISP occurs, and the weary customer service operative informs parental type that their partner requested the block be lifted just last week. Unpleasant arguments ensue. And that’s just if it works. What happens when the filter fails (and it will)?

There’s a massive gulf between “suitable for children” and “pornographic”. Content is not binary in this respect. Is The Sun suitable for children? Not especially, but is it pornographic? What about Page 3? Where does the line fall? How does the line fall? What the hell do you do when your site is wrongly classified?

There are no easy answers, which is why after nearly twenty years of the World Wide Web, this hasn’t quite happened yet.

There are more dubious aspects to it all, too. The official line is that people will have to opt in to the filtering, but this isn’t just a case of having to phone up your ISP to ask if they can put a filter on your Intertubes. No, people will be prompted at sign-up time. You can imagine how this will go:

“Do you have any children in your household?” “Yes… an eight-year-old” “Would you like to protect them from adult material on the Internet?” “oh! that sounds like a good idea”

You get the picture.

You have to wonder how it all ties in—in spirit—with Cleanfeed, which was designed specifically to prevent inadvertent access to child pornography (operating on a strict blacklist basis), but is completely unaccountable and has had its own fair share of foul-ups. We also know that the government is keen on content-blocking as part of the Digital Economy Act implementation work, although has been told by Ofcom that it’s not especially feasible — it’s a lot easier to do if people are having things blocked as a matter of course (I’m not even going to get into other areas of law enforcement where a desire to suppress certain kinds of content has been expressed). How long before all of these threads are tied together, resulting in a massively crap system which causes us all immense amounts of annoyance but continues to be justified with the “oh, won’t somebody please think of the children?” line?

Frankly, Cameron can shove his filter up hisNO CARRIER