f someone had indecent images of 16 and 17 year olds on their PC that had been placed there on or before April 2004 and then they deleted these images prior to May 2004, deleted in the only manor that Microsoft Windows permits i.e., by highlighting the file and pressing delete. Would your Police Force prosecute for the possession of those images?

Re your research there are no hard and fast rules on deciding if some were to be charged , each case is based on it's merits.

Any computer seized from a suspect would be thoroughly examined forensically. The findings from that examination, together with evidence through interviews of suspects and witnesses would be put before the Crown Prosecution Service with a view to determining whether or not any proceedings would be taken against an individual. In other words, decisions on prosecutions are taken on a case by case basis. 

Thank you for your prompt response. However my question is quite clear and does not imply any circumstances other than the ones outlined within the question. If you still state that each case would be taken on a case-by-case basis, this raises some very serious questions for members of the public. The question is quite clear and unambiguous; it does not imply any other wrongdoing. The question only relates to images, which were legal at the time of making and illegal after the law change. One would have to ask the question why all people in these circumstances would not be treated in the same way? If you would like to comment further then please do so, if not, your entry into my final paper will probably read something like this ‘Derbyshire Police charge people committing the same crime randomly based upon a set of circumstances that they are not prepared to divulge’