I am usually split on decisions of security, but this makes no sense at all. Young people have a natural interest in sexuality and it is wrong to think that porn is the root of whatever perceived malaise officials see in British society. Even if that were the case, it is a naive man who thinks any relatively tech-savvy youth wouldn't find their way around it, as the article Mod posted shows. And none of this justifies the intrusion of a government that seeks to replace the role of parents. A poorly thought-out decision.
I read somewhere that British politicians have this process of thinking: "Problem X exists. We should do something. This is something. Therefore, we should do it." This is as good an example as any.