Yes, I realise I sound like Chandler Bing. And I realise that gives away my age. But - parents of teenagers - be aware IT'S SO EASY 
I decided to check my parental controls were switched on - Virgin websafe - and they are. So if I search, as a random example, Pornhub, I get "no search results", just as I should. And if I type in the url Pornhub.com, I get the "Virgin Media has blocked this website" screen. Just as I should.
But as I have teenagers I then switched Safari to pervert private browsing mode and googled "how to bypass pare nxtal controls".
And all you have to do is bring up a free proxy server screen, type in Pornhub and there's the porn. All of it. Two screens away. I DID NOT KNOW THAT.
Ps random xs and spaces are in the probably vain hope that this very thread won't become a resource for those searching.