DO YOU BUY THE idea that evil exists as an actual, quantifiable force? If the answer is yes then by definition your world should be a fractionally less evil place today.

Myra Hindley, the popular personification of evil, is dead. Her body, thanks to the services of Cambridge crematorium, will tonight be reduced to a pile of ashes. It stands to reason, does it not, that if the tabloid high priestess of wickedness is no more then the world must be slightly purer for her passing?

It is unlikely that many people believe this, in the literal sense. For the past 36 years Hindley has been less equipped than the average person to inflict harm on the community and has existed more as a peroxide blonde icon of amorality and malevolence.

Yet Hindley’s crimes were so heinous, so beyond our realms of comprehension, that when she died she managed once again to leave us linguistically impotent. The only way to describe her destructibility was to reach, as always, for the language of hellfire and brimstone.

The Sun declared that Hindley was “The Devil”, no less, its report confidently asserting that she was at last “rotting in Hell”. The Daily Mirror simply called her “A Woman of Evil”. In a different approach, the Daily Mail published a transcript of the tape-recorded last words of the murder victim Lesley Anne Downey, arguing that “only by reading them can we begin to understand the nature of true evil”.

Can we? Do we? By hearing a little girl begging not to be stripped while a flat-voiced Hindley orders her to put the gag back in her mouth so that Ian Brady can molest her, what do we learn about evil’s make-up? And does the fact that something so terrible happened mean that the perpetrators are automatically evil or must they by definition be mentally ill?

A person well placed to answer such questions is Dr Gwen Adshead. For half of her week she works as a consultant psychiatrist at a London trauma clinic, treating victims of violence and torture; for the other she works at Broadmoor maximum security hospital, where the likes of Peter Sutcliffe, the Yorkshire Ripper, are held, and where she has qualified as a consultant psychotherapist.

She sees both sides of extreme cruelty — victims and perpetrators.

A popular modern view is that neurophysics and psychiatry have neutered traditional interpretations of good and evil via the “abuse excuse”, the idea that maltreatment in a person’s past is to blame for their violence in the present.

But Adshead believes that many human actions can indeed be termed evil — and that all of us are capable of committing them. Neither, she says, must the perpetrators be ill, psychopathic or serial offenders. They can briefly enter a psychopathic state of mind then go back to living perfectly normal lives, as did the Bosnian soldiers who raped women then returned home to become model citizens.

“I prefer to use the word (evil) as an adjective, not a noun,” Adshead says. “Rather than an entity out there, it is a state of mind . . . and everybody has the capacity to get into an evil state of mind. There are people in evil states of mind up and down the country, all day, every day. As we speak now somebody is getting it together to smash his wife in the face. Somebody will be getting into a state of mind that may end up in rape. I see people who have been fantastically cruel to their children but they aren’t mentally ill at all.”

Despite its prevalence, though, evil continues to elude definition. It is not, Adshead stresses, a medical term, and certainly not a psychiatric one. It is less a diagnosis and more a term of incomprehension. Morality and theology are required to complete the picture. Even the Oxford English Dictionary gives the spectacularly unhelpful definition of evil as “bad, harmful”, something that could equally apply to speeding.

What most people understand as evil is a particular type of cruel, humiliating, pointless and destructive crime that someone commits against another person when they could just as easily have chosen not to. Unlike a crime of passion or revenge, the victim is almost an irrelevance because the deed is all about the doer.