All UK ISPs have compulsory blocks already - courtesy of the unaccountable CEOPS under the guise of Thinking Of The Children/Child Porn. All sorts of URLs/IPs are blocked (many of which should be blocked because they ARE CP but some are not, just judged by The Powers That Be as being unacceptable [e.g. pirate bay]). There is no way to know what is on the list and no way to find out - anyone inquiring is automatically classed as a CP supporter and subject to investigation.
Coupled with the English removal of right to silence (discussed a few days ago), the UK long ago became a scary place for anyone interested in freedom and justice. [Scotland retains the silence right but don't expect that to help you much.]
We're just seeing an extension of this as people have been prepared already so it is time to extend the state monitoring and intrusion as everyone now believes it is a Good Thing(tm) because they know deep down that they truly love Big Brother.
(edit:spelling, twice. That's embarrassing)