1. Porn filtering is not law in the UK, that is a common misconception. It was merely encouraged by the government, but ISPs are not forced to offer it. The ISPs absolutely are the ones to blame.
2. DNS hijacking certainly is not mandated by law.
Edit: Here is a post by Adrian Kennard, CEO of Andrews & Arnold ISP in the UK, regarding porn filters:
http://www.revk.uk/2014/02/porn-filters-no-it-is-not-law.htm...