What effect is changing porn content having?

The ubiquity of access to the internet means that pornography in some form or other is available day or night in the privacy of anyone's home. In the UK sometimes for a fee, more often for free, you can watch people you've never met doing the most intimate of things for the delectation of their viewers.

But what effect is all this exposure having upon us and upon our children?

BBC Newsnight's Paul Mason examines whether the changing content of pornography, particularly an emphasis on violence and more extreme acts, is affecting how we behave.