I do have to wonder, though - What will the UK nannies do if essentially the entire country opts out and says "Yeah, thanks, but we want our porn and violence, thankyouverymuch"?
That's almost precisely why this is being done in the first place. A Member of Parliament named Claire Perry saw a bandwagon she could jump on, using a tale she concocted about her daughter Googling for cookie recipes and getting porn instead, and used this as an excuse to hold a "hearing" on the subject. The hearing found that most parents were already aware of parental controls, had the option and chose not to use them; she took this as an excuse to push filters harder, demanding that ISPs make them opt-out rather than opt-in in hopes of boosting uptake. (Funnily enough, several of the people testifying at her "hearing" happened to be from companies involved in the filtering business...)
Since the biggest four ISPs agreed to force all their customers to reiterate specifically that they still don't want filtering, hopefully this will be enough to stop these idiots pushing any harder for a while - albeit having forced them to flush money away buying in a filtering system most customers never wanted. My current (much smaller, tech-savvy) ISP is very much opposed to this nonsense, which is one reason I'm happy to be their customer - though unfortunately this has already drawn government attention (after which, they had to take on an extra member of staff and upgrade transit pipes to handle the increased demand - probably not the result the politician expected!)