Any family with a taste for boats will understand the particular horror of what the Darwins did to their sons, and indeed to John's aged father. When someone is missing and presumed lost at sea, the questions in your mind become tormentingly detailed. Was it quick? How long did he struggle? Was he afraid? Did he know it was the end? Does drowning hurt? If you know the person and the boat, it is all too easy to imagine the last minutes with varying degrees of horror.

This I know: my husband's position reports once vanished for 36 hours during the single-handed Atlantic sailing race. Those questions were just beginning to unreel in my head as I sat, late at night alone in the house, studying the Atlantic weather charts, wondering how to tell the children. Then, with a cheerful bleep, I learnt that all was well.

For the young Darwins such awful questions did not go away: they must have inhabited five years of nightmare, pity and sorrow. I can hardly bear to think about it. And all the time their appalling mother was lying to them and planning a ritzy retirement in the sun with her man. Meanwhile, John Darwin - horrid detail - when he came back to hide in the family home found that he “missed his sons”, so told her to put their voices on speakerphone when they rang the sham widow, no doubt condoling and gentle. The supposed corpse of the father stood and listened: not full fathom five at all but alive and happily growing richer.

The whole business is horrible, not only a blasphemy against family life but against the solemnity of death. The final disgraceful note was Anne Darwin's plea of “marital coercion”: as if this adult woman - educated, supposedly religious, responsibly employed as a doctor's receptionist - were some poor terrified teenager trapped in an arranged marriage 5,000 miles from home and speaking no English. Oh yes, these past few weeks it has been easy to get quite carried away with disliking the cruel Darwins, and feeling sorrow for those they duped.

Anne Darwin's performance of a lifetime

Trial for fraud and money-laundering revealed an elaborate five-year-long deceit that fooled many people

Multimedia

• The police tapes

• Pictures: the great canoe fraud

BACKGROUND

• John Darwin's money-making schemes

• Canoe man and Bond boost Panama tourism

• Darwin wife: I wished he had drowned

What bothers me, though, is that the judge seems to have got carried away in the same direction. Mr Justice Wilkie said: “Although the sums involved are not as high as some reported cases, the duration of the offending, its multifaceted nature and in particular the grief inflicted over the years to those who, in truth, were the real victims, your own sons whose lived you crushed, make this a case which merits a particularly severe sentence.”

Hang on, Your Honour. Is that really so? Speaking as a disgusted onlooker, I would have no problem with making the Darwins pick oakum or break stones for a decade. But the law is supposed to be cooler-headed than we disgusted onlookers. It has to be, or we are all in trouble. It seems clear enough to me that two crimes were exposed in Teesside Crown Court in those dramatic hearings, but that only one of them was properly the business of the judiciary: the financial fraud.

The second crime, more horrible to contemplate in human terms but outwith the law's reach, was the deceiving of the sons and the old father, and the mother's cold-hearted willingness to cast her grown children into fake orphanhood and real grief. Vile behaviour, yes: let readers and media condemn, rant and shudder.

But the judge? Come on - lying to family members and causing them misery is a moral offence but not a criminal one. “Crushing the lives” of your adult children with lies does not, as a rule, attract a prison sentence. Ask any victim of a rough divorce.

Wrecking a family one way or another is not uncommon, but is very rarely indictable. We do not lock women up for misleading their offspring (and their husbands) about who is the real father. We do not drag parents into court because they coldly refuse to speak to their gay sons or daughters ever again; we do not throw people into prison because they emotionally blackmail children into giving up a chosen vocation to become personal carers or to work in a dull family business.

Adultery involves lies, betrayal and the breaking of solemn promises but it is not a crime; breach of promise to marry was abolished as a tort in 1970, and you certainly cannot sue people for “alienation of affection” any more. The principle seems to be that private bad behaviour - short of theft, violence or fraud - is simply no business of the criminal law.

I am comfortable with that. If the Darwin sons want to bring a civil claim of some sort for emotional abuse (and I doubt that they would) then that is their business. But the fact is that the judge gave the Darwins a sentence twice as long as that awarded to many who defraud financial institutions or the Treasury on a far grander scale. Three years is a common tariff. Six is not.

Mr Justice Wilkie's statement in court suggests that it was the suffering of the “real victims”, the sons, that swayed him. If he had said that the deceiving of the sons merely convinced him more fully of Anne Darwin's calm intention of lying to insurers and pension funds, fine. But his emotive language suggests something quite different - a conflating of personal revulsion with criminal sentencing. And somehow I don't like that.

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