I'm not sure if my mother, thrilled when I decided to study law, ever anticipated that this would involve me spending weeks in court live-tweeting about fisting and how best to stick metal rods down one's penis. But it's testament only to how extraordinary it is that Simon Walsh's case at Kingston crown court ever reached this stage that I found myself doing exactly this.

I was alerted to Simon's case in July this year. Walsh was charged by the Crown Prosecution Service (CPS) with five counts of possessing extreme pornographic images under Section 63 of the Criminal Justice and Immigration Act 2008. Police officers raided his city-centre flat and took all his electronic equipment on the suspicion that he was in possession of an indecent image of a child. No illegal material was found on any of the equipment, but in an online email account six images were recovered. Five of these were retrieved from his "sent" folder, and one from his inbox. Simon was subsequently charged with five counts of possessing "extreme pornography", and one count of possessing what was purported to be an indecent image of a child. The final image was sent to him unsolicited, and he had no recollection of ever viewing it. It was also the defence's case that the last image was not of a child but an adult male.

"Extreme pornography", according to the act, covers images of any number of sexual activities "likely to cause serious injury to the breasts, anus and genitals". The judge in this case ruled that he considered "serious injury" to relate to "physically, mentally or morally harmful". As Walsh, a barrister himself, remarked over the weekend: "How on Earth can one's genitals be morally harmed?"

The CPS, however, seemed ruthless in their pursuit of a conviction. I'm certainly no prude, but in the process of the trial I learnt more about the anatomy of the anus and penis than I have ever felt necessary. Did you know the difference between an anus and rectum, or that we have not one but two sphincters? Or that urologists occasionally have cause to extract ballpoint pens from people's penises? Neither did I. I never thought I would witness a barrister for the CPS refer so many times to "Nasty Kink Pigs" (a sex contacts site) in legal argument with apparent relish, nor an expert witness utter the immortal words: "It may take some time for someone to take a whole arm into their rectum." I didn't think I would ever see a consultant urologist be asked to stand in a witness box and demonstrate how to hold a penis using a ballpoint pen casing. All these details were supposedly essential to the CPS's case, attempting to prove that the images showed adults causing "serious injury" to each other's genitals and anuses and that Walsh had a keen interest in viewing pornography of this kind.

Nonetheless, interrogating a defendant about their most intimate and private sexual fantasies and activities is exactly what Section 63 permits a prosecuting barrister to do. The same barrister reminded the jury in his closing speech that this is not a Victorian law, but came into force as late as 2008. Yet a jury is still obliged to come to a decision as to whether or not pornographic images are "grossly offensive, disgusting or otherwise of an obscene character". As the judge presiding over the case said in his directions to the jury: "I don't pretend for a moment that these parts of the legislation are easily understandable".

It becomes difficult to imagine, after Simon Walsh's landmark acquittal on all counts, under what circumstances charges relating to possession of extreme pornography may be brought to the crown court again, but it seems the CPS has a rather prurient interest in bringing other people's private sex lives to light and persecuting them for it.

At one point in the trial, the prosecuting barrister asked Mr Datta, a colorectal surgeon at Guy's and Thomas's NHS Trust: "Can you tell us what a douche is?" Perhaps the CPS might be able to answer that question.