The amount of misinformation spread about this mythical "UK porn filter" is astounding, but I guess unsurprising as it fits completely into the orwellian surveillance state conspiracy theory agenda.
Cameron is pandering to worried parents who believe the internet is a bad place, and little Johnny must be protected by a filter. The government believe it will mean they'll win the next election. It's just politics.
It's nothing whatsoever about censorship. Anyone can opt out of the filters, and anyone can get past the filters with a couple of clicks.
edit: anyone downvoting actually live in the UK? Any of you actually have any hard facts? Or are you just regurgitating the crap you read on the internet.