After the death of Princess Diana, Britain's newspaper editors vowed to clean up their act. They would am end their code of practice and stick to both its letter and spirit. Within months, several of them are treating that code with contempt.

One clause is specific: "Payment or offers of payment for stories, pictures or information, must not be made directly or through agents to convicted or confessed criminals or to their associates . . . except where the material concerned ought to be published in the public interest and payment is necessary for this to be done."

Yet newspapers have paid for the serialisations of books about childkiller Mary Bell and murderer Sean O'Callaghan; they are about to pay for the stories of the British nurses convicted of murder in Saudi Arabia, and at least one paper has offered a huge sum for the story of Louise Woodward, the British nanny found guilty of manslaughter in Boston.

During the press's internal post-Diana debates, no editor spluttered with quite the same passionate outrage about falling ethical standards as the Daily Telegraph's editor Charles Moore, but his noble crusade is looking particularly hollow now.

When the Times announced that it was to serialise Cries Unheard, the controversial book about Mary Bell by Gitta Sereny, Moore rushed into print to boast that as a matter of principle, he had rejected the idea of serialising it even though his senior staff had made a provisional deal to pay the publishers.

In explaining his decision and casting aspersions on his main rival for having had the temerity to do the opposite, Moore wrote: "The book was well-written. Its author was respected. Its subject matter was sensational and might therefore be expected to sell more newspapers, but there were other considerations. What about the families of Mary Bell's victims?"

Though the book was undoubtedly serious and responsible and its publication could be defended in the public interest, Moore argued that "the net effect of our serialisation would be that Mary Bell would end up with more money than would otherwise have been the case . . . I felt this was a situation that a quality newspaper such as the Daily Telegraph must avoid".

So far, so principled, but these ethics were, it appeared, tempered by commercial considerations. Moore said he was "worried that a minority of our readers would be so angry at the idea of any platform . . . being given to a child-murderer that we would face a serious problem". In other words, a possible boycott and a fall in sales.

That weasel qualification was bad enough, but it was as nothing beside the bare-faced U-turn performed a fortnight later by the Daily Tele- graph. In announcing the start of its latest book extracts (for which it paid a reputed £35,000), its leading article last Saturday trumpeted: "Today we are proud to serialise a book entitled The Informer by Sean O'Callaghan."

Proud? To pay O'Callaghan? What overriding principle convinced Moore that this, rather than the Sereny book, was worth serialising? Implicitly, the leader suggests it was because he was truly repentant, he had voluntarily given himself up to the police, he had prevented deaths by informing on the IRA, he was a hero. Explicitly, it stated: "It is because of O'Callaghan's services to the truth that this newspaper is serialising his story and paying for the serialisation in the ordinary way."

Service to the truth? Perhaps Moore doesn't know quite as much about O'Callaghan as he should. For the record, this is what the truthserver told the High Court in Dublin during the Sunday Times libel trial. Under cross-examination, he was asked to name any one person in the last 10 years to whom he had consistently told the truth. O'Callaghan replied: "It's extremely difficult to give you that answer."

What public interest is satisfied by publishing several hundred words of allegations by a man who claimed in several interviews to having murdered John Corcoran in Kerry in 1985 and, in court, admitted he had perpetrated a lie on the flimsy excuse that he was trying to get the death properly investigated?

In what way does it enhance a "quality newspaper such as the Daily Telegraph" to deal with a man who has admitted making false statements to both the RUC and the Sunday Times, organisations which he purported to be assisting?

Consider other relevant differences between the O'Callaghan and Bell cases which surely make the serialisation of the book about her much more sympathetic. His crimes were committed when he was a supposedly rational adult. He was given two life sentences but was released after just eight years because of his services as an IRA informer. Bell, who was convicted of the manslaughter of two children when she was aged just 11, served 12 years.

The justification for carrying her story was clearly put by the Times editor Peter Stothard: "Only by trying to understand what could conceivably have driven an 11-year-old girl to kill two small boys . . . can we come any closer to stopping these crimes."

Given his admission of telling lies, it is more difficult to divine genuine reasons for the O'Callaghan story which the Telegraph has publicised as "an illuminating first-hand account of how the IRA works, thinks and feels". But what is true and what is false? Where is the corroboration for his claims about meetings in which he asks us to believe he can recall not only every individual in ttendance but verbatim quotes?

By these standards, the ethical dilemma facing the two tabloids which have signed up the nurses Lucille McLauchlan and Deborah Parry is reasonably straightforward.

The Daily Mirror and the Express argue that the women did not receive a fair trial in Saudi Arabia and that their confessions were extracted unfairly. Therefore, there is a public interest in telling their stories.

If the nurses did not murder their colleague, Australian Yvonne Gilford, as they have always maintained, the papers can justify paying them on the understanding that they deserve making some money after their ordeal and spending 18 months in jail. That is, of course, a big if.

By accepting their version of events at face value, the papers are suggesting that all trials outside Britain are flawed, cannot be guaranteed to give justice and convicted Brits must therefore be innocent. Publishing these women's stories in Britain, however, is different from the Bell and O'Callaghan instances.

The victim's relatives live on another continent. They may well have suffered an injustice and we cannot deny them their freedom to speak.

This freedom may be tainted when papers pay but, while many may view the deal with disdain, one can hardly intervene in the operation of the free market in such a competitive climate as the British newspaper industry.

The Louise Woodward case is different again. Unlike the nurses, she was tried in open court, every minute televised, under a judicial system which Britain generally regards as fair. For a paper to pay her, if she remains a convicted person, would be wrong.

Funny, though, how British newspapers never fought with each other to offer money to the innocents who lingered for more than 20 years in their own jails. Was it not in the public interest to hear about the unjust tribulations of the Birmingham Six and the Guildford Four? Perhaps the highly principled Charles Moore can explain why not.

Roy Greenslade is a media commentator with the Guardian