ACPO (the Association of Chief Police Officers) lead on Extreme Pornographic Images, Jim Gamble, Chief Executive for CEOP (the Child Exploitation and Online Protection Centre) issued a statement (in full here) that included
"the new criminal offence of possession .. reflects the potential damaging impact that the possession of this material could have." which does at least acknowledge the lack of clear evidence linking images and damage.
ACPO went on " This is not intended to infringe upon the personal lives of citizens or dictate their lawful sexual activities. This is about countering material that is sexually violent and illegal in nature and not about affecting one's civil rights and liberties" but of course it is legal to simulate but now illegal to make images of those simulations for others to view.
ACPO's statement to backlash is not quite as categoric as that quoted in a somewhat
tendentious article in the Guardian, to wit ACPO said "The police will not be actively targeting members of the public but will be conducting investigations into the unlawful possession of this material where found."
It is likely that the enthusiasm with which "criminals" are pursued will vary from force to force. Certainly in their responses to the consultation in 2005 some forces were very gung ho.