BT, Sky Broadband and Talk Talk have implemented opt-out Network level filtering for their customers.

The thing is, as well as overblocking websites that should not be filtered the ISPs have poorly implementated their block pages.

http://makeyourispblock.me/ was registered at 2am on the 22nd of December but due to the badly designed block pages it can be made to be shown as blocked.

Sky Broadband Block Page
BT Broadband Block Page
Talk Talk Broadband Block Page