Many UK ISPs have "adult content" filters, which tend to be wide-reaching and block a lot more than just porn sites. But these are optional and can be turned off very easily.
There's a smaller set of non-optional blocks (pirate/torrent sites) which you need a VPN to get around.
This seems to be just another small step towards a future where only pre-approved websites are accessible via the method most people will use. It will not be called banning, this is just a measure to "ensure that the content we are serving to our users is held against our high quality standards" or the classic "it's to protect the children" or to "condemn terrorism".
Porn is not really Illegal, just unwanted, which is apparently reason enough to block it. Does this mean any content which is "unwanted" can be blocked just like that?
I have a theory that the ISPs over-block with their adult content filters, so you've got plausible deniability and don't have to ring up and say "I want porn please." Because the alternative is that they lose a customer to an ISP who doesn't embarrass them.
There's a smaller set of non-optional blocks (pirate/torrent sites) which you need a VPN to get around.