As a journalist whose revelations changed the course of British history and made him a multi-millionaire, Morton has always attracted envy and resentment. But I write as a former devout Mortonite, one of the relatively few reviewers who took his book, Diana: Her True Story, seriously from the time of its publication in 1992. My interest was based on the assumption that the book was ventriloquism for the princess. Accordingly, it was relief rather than resentment I felt this week when Morton's admission that the book was indeed a disguised autobiography revealed his strenuous denials to me in two separate interviews (in print and on television) to have been lies.

Morton isn't a moral leper because he lied then. He is a moral leper because he has chosen to tell the truth now. The writer's decision to republish Her True Story with first-person quotation replacing third-person nuance - and his apparent release to America's People magazine of the tapes the princess made for him - raise two issues of media behaviour, which are at least as important as the currently much-discussed question of privacy: the first is confidentiality; the second is commercial exploitation of tragedy.

Other professions, which offer safety deposit boxes for conversation, would expel members who behaved as Morton has. The Catholic priest is not freed from the confidentiality of the confessional by the death of the penitent, nor is the lawyer's duty of secrecy suddenly dissolved should the client happen to misjudge the speed of a bus outside the court.

Perhaps journalists have never aspired to the standards of the Church or the law. Even so, it would be surprising if journalism courses teach that confidentiality is merely a lifetime guarantee. It seems unlikely that those reporters who have risked imprisonment by refusing to identify a source would have made an instant phone call to the judge if they recognised in the obituaries column one morning a name they had carefully omitted from their contacts book.

Cynics might have assumed that Morton would use the traditional defence for invading privacy or breaking confidences: that celebrities like Diana have a complicated relationship with secrecy and revelation. (Earl Spencer's apparent failure to say goodbye to Hello magazine in recent years lends further credibility to this popular excuse.)

Yet Morton has opted for a more noble apologia. In an interview with ITV's Richard & Judy yesterday, he explained: "I've got a responsibility to people out there who want to understand Diana." This, then, is public service publishing. And yet so many of the public find reading a chore. The British government was forced this very week to launch an anti-illiteracy drive. How long before Morton feels that it is his responsibility to release the tapes to an American television news show or to authorise an audio-book version of the princess's words?

The author's second line of defence raises the wider and more complex matter of commercial exploitation of tragedy. The writer clearly feels that he is being used as a lightning conductor for a general storm of morbid money-making. Also in conversation with Richard & Judy, he complained: "Lord Deedes has written a book! The BBC have released a video! ITN have released a video!" In other words, Morton is no more or less immoral than three ancient media institutions.

In fact, Lord Deedes has written only an 800-word preface for a collection of Daily Telegraph reports, all profits from which will go to the paper's own appeal for the victims of landmines. Such publishing arrangements contrast starkly with the deal by which an unspecified percentage of Morton's profits go to charity.

The BBC and ITV are also a bad comparison, although for different reasons. Both, it is true, are making only a donation from the sales of the video releases of their coverage. But the BBC spent millions from a hard-pressed budget in covering the story on the scale that its licence-payers were perceived to want. ITV suspended adverts during much of the coverage, thus reducing profits. There would be a good case for both broadcasters taking all the proceeds from the video sales to restore their income.

Yet the charge of making cash from catastrophes is more complicated than it might at first appear. In an unusual case of a pop star setting the highest moral standards, Elton John established early on the model of altruism by closing his pockets to any proceeds from the sale of his Diana song. Andrew Morton has now stuck a flag of equal size and prominence in the bogs of the moral low ground.

Morton, however, is right to suggest that there are fascinating shades of commerce between those two positions. Florists - many of whom will be able to retire earlier than planned to tend their rose gardens as a result of the bouquet-mania of September - have been under curiously little pressure to pledge their windfall to good causes. London hotels had their busiest September in history as a result of the funeral, yet the Hilton and Holiday Inn profits are subject to no opprobrium.

Long before the events of the last month, it's clear that public tragedy has built and furnished many fine private houses. Books, television programmes and films on two world wars, the Holocaust, Aberfan, Hillsborough and Dunblane have been sold around the world to the financial benefit of their creators.

Andrew Morton is right to say that there is nothing new in turning death to credit. But this defence cannot protect him because he is also guilty of a novel immorality in deciding that promises of confidentiality are not posthumous.

I'd be tempted to release the full tapes of our past interviews but, unfortunately, he was clever enough to tell identical lies on and off the record.