Eighteen months ago I agreed to write the official account of the life of the Gloucester murderer Frederick West. What I did not appreciate when I began was the intensity of feeling that West and his crimes can provoke in this country.
I had been working for only a few weeks when my book became front-page news. The Independent headlined the fact that I had been given access to West's police interviews, his interviews with his original solicitor, his own 98-page memoir, as well as thousands of pages of other material, by the Official Solicitor to the Supreme Court.
There were questions to the Prime Minister in the Commons, headlines - both tabloid and broadsheet - radio phone-ins and television interviews: it was a media circus. My book was "exploitation", "outrageous", "deplorable", and it was my fault. When the storm subsided, I went back to work.
West's story is serious, painful, and at times, terrifying. I tell anyone who asks me not to read it late at night, and to remember that they can put it down. But I also tell them that Frederick West was no mad loner, no psychopath. He did not hear voices, he killed for pleasure, and sexual pleasure in particular. West was an evil man whom we cannot afford to ignore.
This week the news broke that a film might be made from my book and the official archive upon which it was based. Though the agreement to option the book to the Portman Entertainment Group had been reached by the Official Solicitor, I was once again the single public face of the decision.
Within minutes of the story breaking I was being told that the decision to exploit this material was "sick", "perverted", "exploitative", "prurient" and "wrong in every way". It made me wonder what it was about West that made the reaction so ferocious, and, finally, I think I have begun to understand.
Frederick West touches a particular nerve in British society that makes us uneasy and defensive. In particular, it is the sordid sexual aspect of his crimes that so unsettles us. West shows that beneath the surface of a respectable English cathedral town, there lies a world of prostitution, contact magazines, sado-masochism, pornographic films, bondage, leather masks and sexual aids.
No matter how much we may wish it otherwise, there is nothing discreet or respectable about West's crimes. They explore the basest and most depraved elements in human nature - and what is profoundly discomforting to the British is that they happened where many of them would be happy to live.
Half a century ago, George Orwell wrote of the classic English murder that it was always a matter of class. Orwell saw the passion for reading about murder in the Sunday papers as "the desire to gain a social position", or at least "not to forfeit one's social position". He concluded that no other kind of English killing "would be so long remembered as the old domestic poisoning dramas, product of a stable society where the all-prevailing hypocrisy did at least ensure that crimes as serious as murder should have strong emotions behind them". That is no longer true.
Frederick West demonstrates conclusively how much English society has changed in the past 50years. For sex was his motive, sex and the control of innocent young women whom he did not want to ever leave him, sex and the power that it gave him over his wife and family, sex and the fascination it held for so many men and women who came into contact with him. That is what makes West so potent and painful a symbol in Britain that the suggestion that a movie might be made flares into controversy.
The same is not true in Australia. Last November, I spent two weeks there promoting the book, and the reaction was precisely the opposite. I detected no embarrassment, no discomfort, just an appetite to try and understand why West acted as he did, and how he got away with it for so long.
One lunchtime I appeared on one of the country's highest-rated television shows - neither the time nor place, I would have thought, to discuss such terrible crimes, but Kerri-Anne Kennerly, the interviewer, never doubted that the millions of housewives in her audience should be made aware of what evil this man was capable of. "I'm sorry I couldn't bring myself to finish it," she whispered during the commercial break, "but I'm glad you wrote it, somebody had to. We need to know."
And in Australia there was no embarrassment about the sexual element of West's crimes. "There's nothing to be ashamed about," one magazine interviewer told me wearily. "I don't see why the English get so het up about it." Philip Adams, who runs a nightly radio programme, and is also one of the creators of the Australian film industry, even told me on the air that a film about the case was inevitable and that I should get involved "to make sure the film-makers do it responsibly". His words have been ringing in my ears all week.
Back in England only a few weeks later, everything is different. The idea that a film might be made of West's life is considered horrifying. I respect the objections, but I cannot escape the feeling that they demonstrate a desire to sweep West's crimes under the carpet. He threatens a very British illusion that we are not a society which, in some parts at least, is fascinated by the darker borders of sexuality.
Frederick West's crimes underline the fact that, although we may be reluctant to admit it, sexual experiment is one of the themes of contemporary Britain. If you doubt this, cast an eye over the small ads in the broadsheet newspapers. Why else would so many commentators have assumed that a film about his life would necessarily be prurient and titillating?
Because he took pleasure in secret vices, and carried them to horrifying and fatal extremes, West is a disgrace to the nation. But it is, perhaps, even more terrifying to think that one reason why he went undetected for so long is our deep reluctance to admit that such a crime has happened here. It is our secret shame, and Frederick West thrived on our embarrassment.