Just last month Google and Microsoft came together in an unlikely pairing. This was not a software venture, but a bid to help tackle the problem of child porn online. UK Prime Minister David Cameron has said on numerous occasions that ISPs needed to do more to not only block access to torrent sites -- despite the fact they can be used for perfectly legal downloads -- but also to make it more difficult for children to access pornography. Four major ISPs either already have porn filters in place, or have plans to roll them out.

TalkTalk's filters have been in place for a few years now, Sky's were recently launched and Virgin is piloting a scheme due for full scale roll out at some point in 2014. In the past few days, BT switched on its filters, falling in line with government requests for access to legal porn to be made opt-in -- i.e. blocked by default. So is this having the desired effect? Well, it's very early days, but there are a few observations to be made already.

Firstly, the porn filters apply to new users. Anyone joining BT for internet access will find that the porn filter is in place by default, and they'll have to phone up to get the block lifted if they find that it is interfering with their ability to access the content they want to see. Secondly, it has been very quickly revealed to be a "sledge hammer to crack a nut" solution to a problem -- it may be working to some extent, but there are also some unwanted side effects.

The idea of the filter is to prevent children from -- innocently or otherwise -- viewing online porn. But if there's one thing we know about children, it is that if they want to access something, they will do so. Knowledge of proxies and filter bypassing tools are no longer the domain of the technically-minded -- it is the norm. PirateBay is blocked? So what! A quick re-route and 30 seconds later the site is accessible again. Hooray! The same is true for porn or anything else that may be blocked.

Talking about children and pornography in the same breath is always going to raise a few hackles (even if we're not talking about child porn per se), but any form of filtering is flawed from the start. My fear with filtering is that categorization of sites -- the millions and millions of sites that exist -- is all but impossible. Tests carried out by BBC TV show Newsnight found that with 68 test porn sites, TalkTalk -- the longest running filter -- failed to block 7%. With new sites popping up every day, shifting servers, changing names and disguising themselves, achieving 100 percent porn blocking is all but impossible.

But there is a more worrying concern: that these filters block more sites than they are meant to. And this is exactly what is happening. The porn filters that have been put in place are also blocking access to genuinely useful sites. Sites such as sex education programs, pages about getting help with domestic abuse, and even a rape help center. What is worse? Allowing a child to access porn, or preventing them from accessing sites they might need? It seems the two are not mutually exclusive.

We run the risk of creating another Great Firewall of China, a two-tier internet. Yes, children should be sheltered from adult content, but a less drastic solution needs to be found. If Microsoft and Google can work together, why not ISPs? The government understanding of the role of the internet, and appreciating children's knowledge of it, is sadly lacking. If the web is to be filtered a proper, fully funded taskforce needs to be behind it, not a disparate group of ramshackle ISPs all working independently on different systems.

It's great that David Cameron and BT bosses can go to sleep with a smile on their faces in the belief that they're doing something to help. But do the disadvantages outweigh the benefits -- is this the best approach?

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