Jack Straw sees paedophilic imagery…

Can someone explain this to me? If merely having images of a paedophilic nature on one’s computer is a crime (no matter the context), then how can Jack Straw say, “I’ve seen some of the exhibits – if you can call them that – that are available on the internet, that are run by paedophiles. They really are absolutely appalling” without being promptly arrested? Any decent civil liberties group should be pointing the police in the direction of his PC.