Was Andrew Morton right to have fingered his subject as the source, indeed part-author, of Diana: Her True Story? The eager buyers in the bookshops yesterday seemed glad enough to part with their money, but Mr Morton was given a roasting by the tabloid papers for "the final insult" to the People's Princess. Much of this amounted to brazen hypocrisy, condemning Mr Morton on page 1, with full details of his revelations on pages 5,6,7, 8 and 9.

But there is a serious issue of principle here. If journalists are given information in confidence, are they entitled to break that confidence if their source dies? The answer must be, unequivocally, yes. Diana's role in making her story public cannot be taken to her grave. If in five years' time a historian sought to tell the story of the modern royal family, and interviewed Mr Morton, he would have been quite wrong to continue to conceal her involvement with his book. The sense of unease arises because he has chosen to unlock his secret files barely a month after her death. But to say that Diana would have wanted her part in her public relations operation kept secret, and that her wishes should be respected, is to confuse a matter of taste with one of principle.

The law of confidence, like the law of libel, cannot be enforced after death. People can try to preserve family secrets after they die, but they cannot rely on it, especially if they have used a journalist to reveal them - at arm's length - while they were alive, as part of a campaign to influence public opinion.

Mr Morton would have been wise to resist pressure from his publishers for a few months, because people in their present mood of reverence for Diana are properly and understandably offended. He could certainly have afforded to hold off - his book has already made him rich.

There is something unseemly, too, in his selling the tapes of Diana's interviews-by-proxy which she recorded for his book. Splashing them across an American gossip-sheet is no way to show respect to the recently departed. The timing and method of publication are indecent; but publishing them at some time, in some way, would not have been wrong. On the contrary, it would be quite wrong to suppress the contents of the tapes, in the long run. Diana's estate may well be entitled to argue in law about where the proceeds from the sale of her words should go, but it should not be allowed to prevent their publication.

We see the personal effects of famous or public figures sold to the highest bidder all the time. Was it wrong to sell John Lennon's letter to his first wife, an intensely private correspondence which touches on the sensibilities of the living, namely their son Julian? The publication of personal letters and recollections of countless literary figures has caused distress to people who are still alive.

Measured against these examples, the capacity of Mr Morton's revelations to hurt those who were close to Diana is muted. We already knew that she had effectively authorised the book. Mr Morton has merely demonstrated that her approval went a lot further than being merely tacit: it was utterly complicit. But the fact that she was involved in some way was made plain by the Princess herself when the book was published, and the certainty that it was indeed her true story grew as time passed.

The new element introduced by the publishers is the addition "In Her Own Words" to the cover of the new edition. We have discovered that much of the book was effectively dictated by her, and that the proofs were corrected in her handwriting. This is of significant historical interest. It is not merely part of the soap opera of the royal family, it is part of the history of this country's rapidly-changing constitution. As keeper of a personal secret, Mr Morton should have waited for a proper interval.

But he is in possession of history, which we have a right to know.

Indeed, the revelations confirm Mr Morton as an outstanding journalist. He scores no marks for humility, claiming yesterday that his was the "scoop of the century". Like many good journalists, he can be lambasted for a certain arrogance, as well as patent insensitivity. But he deserves our admiration for having dug out a great story and told it well. No Kitty Kelley he. He did not rush to print second-hand rumour masquerading as in-depth research. He did not traipse around people who had once shaken hands with the protagonists re-telling what "some say" and "others speculate". He got the story copper-bottomed, and we can now see quite how thoroughly it was nailed into place; we can also see why, after enduring a blizzard of establishment rubbishing (the fate of many excellent and accurate scoops) his book has stood the test of time. So much of the story was so extraordinary at the time that it was easy to disbelieve it. But it was true, and now we know just how true. So, this week's revelations mark Mr Morton's ultimate vindication as a story-getter. If only they had come next year. History could have waited a while.