UNTIL a couple of years ago, Andrew Morton was royal correspondent of the Daily Star. Along with a couple of dozen other palace-watchers, he spent 10 years being herded in and out of press coaches searching, usually in vain, for something new to say about the Royal Family. The job requires a degree of sycophancy towards courtiers and, on the rare occasions when the press actually meets the royals, emollient deference.

Morton always had more to offer than that. Another royal-follower from a decade ago recalls: 'Unlike most people, Andrew did sit down and think hard about where the monarchy was going and what it meant to people. Everybody else skated along on the gossip of maids; he made friends with people who were their friends. He latched on to what the real story was, and worked out its constitutional reality.'

Nowadays Andrew Morton is himself the focus of press attention. Does he enjoy this reversal of roles? 'Well,' he says, flashing a smile worthy of a Kennedy, 'it means I have the satisfaction of talking to people like Angela Lambert.' Clearly he hasn't lost his touch.

He was featured in the first issue of OK] magazine alongside such celebs as Ruby Wax and Jackie Collins. The photographs of his north London home were taken with the sort of estate agents' camera that makes rooms look extra spacious. With its buttermilk walls, ruched curtains and great bowls of flowers, his lounge offered more than a nod in the direction of royal decor. Another photograph showed him sitting on a wall of books: each a copy of his own mega- zega best seller, Diana: Her True Story, which sold to 24 countries in 20 languages, including Bulgarian, Indonesian and Taiwanese.

I pointed out that the issue of OK] in which he featured also carried an article headlined 'After the break- up: who's supporting William and Harry?' It concluded that the young princes were closest to their personal detectives - burly chaps in their thirties, perfectly good father material but not actually their father. Could this in part be a consequence of Morton's book?

'Nothing's changed,' he said robustly. 'Royal children have always been closer to their bodyguards than anyone else, because those are the people they see most. Prince Edward used to call one of his bodyguards 'Dad'. ' He went on to tell me a scurrilous, unprovable and unprintable tale about one of the Princess Royal's personal bodyguards. Andrew Morton seems very well-informed: but are any of his tales true?

The public belief that Morton's book came closer to the real truth about Diana than any previous version earned him millions of pounds. (One? Two? Three? Who knows? It's a secret between him and the taxman.) He stresses his unique inside sources in the acknowledgements: 'Many of the Princess's family, friends and counsellors agreed to be interviewed, many of them for the first time . . . laying aside the ingrained habits of discretion and loyalty.' Among those thanked are the Princess's brother ('for his insights and reminiscences') and a bevy of intimates from the inner circle. Morton goes on, tantalisingly: 'There are others whose present positions preclude them from being officially acknowledged for their invaluable assistance. Their unstinting guidance has been priceless.'

Who can they be? Is there a verbal clue here? Morton has steadfastly claimed not to have had information directly from Diana herself although Nigel Dempster, for example, says that of course she spoke to him. Whatever the truth, she could hardly fail to be aware of his researches, considering that he was chatting up her closest friends. Had he ever met her?

'Only at the parties given for the press at the end of a royal tour, where the conversation is usually light, bright and trite.'

And the Prince of Wales? Surely Morton did not talk to him? Given the book's tart dismissal of the heir, it seems improbable. 'I didn't come to dislike him in the course of working on the book, but it very quickly became obvious that both sides were at each other's throats and I would have to settle for keeping the lines open to one or the other. So the views in the book are her views, as related by her friends. It broke new ground, but it cannot tell the whole story.' He pauses, his eyes alight. 'What I'd really like to know is Camilla Parker-Bowles's version. I just hope she's preserved all the letters and diaries, because it will be a real loss for posterity if Camilla's story is never told. One would love to know how much she - or he - wanted to marry. Suppose Prince Charles and Diana divorce in December 1994 and he marries Camilla . . ? We just don't know.'

How about the Princess's two sisters? He does not say whether he talked to them. Their closeness to the Queen - both their husbands are courtiers from the inner circle - would preclude that indiscretion being openly admitted. Butlers, nannies, servants at Kensington Palace? People entering royal service have to sign a vow of perpetual silence. This would prevent Morton from acknowledging the confidences of footmen.

Why did people talk so freely to Morton? One close friend of the Princess says in the book: 'It was painful for us all to see a delightful candle (meaning the Princess of Wales) being progressively snuffed out by the royal system and an empty marriage.' How gratifying for an author to be able to embark on a guaranteed best seller with a clear conscience, even a sense of gallantry, and from unimpeachable motives]

And now, after all the research, what does he think the Princess is really like? 'The real person has low self-esteem and is socially disadvantaged. She was a high-school dropout who left school at 15 with no qualifications. She did a series of menial jobs before getting married very young. She read Barbara Cartland novels and that's what she expected to find in her marriage: love, romance, passion. When it didn't happen she developed neurotic symptoms and malfunctioning behaviour. She is typical of women in the caring professions, who are more likely than others to read Mills & Boon and have eating disorders.'

As late as November 1987 - by which time, Morton claims, the royal couple no longer shared the marital bed - he was writing in the Star: 'It is an often rumbustious partnership, in which a sloppy kiss and a bear hug will follow a battle of wills. Their rows are spectacular but short-lived.'

The truth was that by 1987 Prince Charles was spending much time with Camilla Parker-Bowles, and Diana's circle felt it was time to tell her side of the story, 'the flip side of the fairy-tale'. Morton was the lucky man selected to write it. Asked about his motives, therefore, he retreats into the passive. He did not choose to write it: he was chosen.

I asked Morton whether the Princess had no responsibility, as role model to millions and patron of numerous family-oriented organisations (Relate, formerly the Marriage Guidance Council, is just one), to keep her marriage going? This was surely as important as being seen to visit the sick, the dying, the handicapped, the winners of awards for bravery and the losers in life's genetic lottery? Morton bridled.

'Should she have sacrificed herself, in a situation in which it seemed there was no redress and she was being perceived by the public as an adoring wife and mother when the reality was a daily diet of misery and unhappiness? When the separation was announced, it was a relief to both parties.'

Diana constantly parades her devotion to her sons. Leaving aside her duty as a national icon, doesn't she owe it to her children to maintain a united parental front?

No, Morton says in the book; the Princess was living a sham and her boys needed protection from the extended family they were born into. What evidence is there for this?

'Why did the Duchess of York also decide that she wanted to leave the Royal Family? Could there be something wrong with that family and the way they live?'

Here we come to the heart of the Morton thesis. He believes that the Royal Family is cold, unloving even to its own members, unwelcoming to outsiders, out of date, out of touch, badly advised, and wasting its potential. He is no republican, but: 'The most satisfying thing about the response to the book has been that people have for the first time taken the monarchy seriously.'

So Morton is a kind of 20th-century Bagehot re-examining the role of the monarchy? 'I would agree with that, yes. The ideology of the monarchy has been undercut.'

If that claim sounds immodest, or even ludicrous, it must be said again that Morton knows his royal history backwards and has thought long and hard about the constitutional role of the monarchy.

Since 1983 he has written - well, he said 10 books about the Royal Family. Only eight titles were listed in a library catalogue, so I rang him to ask about the other two. One turned out to be a guide book for Fodor, written anonymously, and the other was his research on Alastair Burnet's book about the Yorks' wedding. They sold extremely well.

So why the royal obsession? His background contains few clues. Morton was the son of a picture framer, the eldest of four children brought up on the outskirts of Leeds. He was a clever boy who went to Leeds Grammar School and from there read history at Sussex University. He became a trainee journalist with Mirror Group Newspapers after which he worked chiefly as a court correspondent. He would rather have been a political reporter, he says. He had already written four books when in 1988 he decided to set up his own business called Palace Press, offering background research and information on the royals.

He is 40 this year. Oddly enough, he very much resembles Prince Andrew (although he is taller), and he shares royalty's facial expression of perpetual, polite interest.

He has been married to his childhood sweetheart, Lynne, for 15 years and they have two daughters. The family moved into their present house in Muswell Hill, north London, 11 years ago, and despite the millions he has earned, Morton says his lifestyle has not changed. He still cycles to work. He still votes Labour, and is an active member of his local party.

After we had been talking about the royals for over an hour, I said: 'Isn't all this very tedious for you? You must have had this sort of conversation a thousand times.'

'Well, I daresay royalty must find the sea of faces tedious after a while,' he said. 'But I've written a book that's become a best seller and a subject for debate and it's beholden upon me to discuss it. Until the 1980s the monarchy just had to be; now it has to do, and that's a basic tension.'

What next for Andrew Morton? 'I've only just finished selling the video, the book and the film. Now, for something totally self-indulgent, I'm doing a history of art course - Holbein to Hockney.' And the next book? He grins that wide frank grin.

'Diana: Free At Last? No - I'm kidding. Not enough has happened at the moment to warrant another book.'

Could Diana lose her appeal?

'Yup,' he says decisively. 'At the moment she's the most popular member of the Royal Family, but if she's always seen as battling against the Palace then her status will subtly diminish and her popularity become compromised. Already she is no longer defined as a perfect person (young, innocent, docile, loyal) but as a vulnerable and flawed human being.'

So why did he write the book? He shrugs. 'I read several biographies written for her 30th birthday which didn't go beyond the cardboard cut-out and I just wanted to know what the real person was like, behind the tiara.' And did he get it right? 'Those who know her well say it's a reasonably accurate portrait.' Of Diana as she was. The post- Morton Diana will be a very different creature. Meanwhile, the post-Diana Andrew Morton is a much richer man.

This is the first in a series of interviews by Angela Lambert. Hunter Davies returns in the autumn.

(Photograph omitted)