edit because HN won't let me post a rebuttal to the reply below:

Private corporations can be compelled and coerced by the government in other ways that aren't readily publicized. If you think these companies enjoy wasting resources on porn filter then you're crazy. Wikipedia:

"Prime Minister David Cameron made it clear in July 2013 that his aim was to ensure that by the end of 2013 all ISPs would have a filtering system in place.[13] As a result three of the four major ISPs (TalkTalk, Sky and BT[14]) began applying default filtering to new customers in 2013[15] with the fourth major ISP, Virgin, doing so in February 2014.[16] Default filtering of existing customers was implemented by all four major ISPs during 2014 with the aim of ensuring that the system applied to 95% of all households by the end of the year.[17][18]"

This timing isn't a big coincidence. Elect a better PM (or indirectly elect considering this is the UK) if you don't want such shenanigans.