I'M A BIT worried about A N Wilson and the Princess of Wales. Could his love be on the wane, could five years of blind adoration be coming to an end, or is it simply a passing depression, brought on by January flu, stuck in his bedroom, stuck with himself, feeling sorry for the world in general?

No sign of any get well Andrew cards, kiss kiss, your affectionate Diana. In fact, no sign even of her photograph.

Couple of snaps of Jesus - with whom he was in love for many, many years - on the wall. Lots of family photos on a shelf, but on the whole a fairly spartan bedroom, faint smell of mothballs or perhaps TCP, bare wooden floors painted white, old-fashioned iron bedstead, hardly big enough for him and his new wife, let alone for all that tap tap tapping, which he is wont to do in bed, turning out his 20,000 words a week of fiction, biography and journalism on his old portable typewriter.

'It is very complicated being in love with her,' he said, his body slowly sliding down the bed.

His deep, dated, upper-class voice sounds funny, coming from such a thin, weedy body. On his bike, which he keeps in the downstairs hall, and wearing his Edwardian hat, he can look quite rakish, the dotty don, the curious curate, but slumped on his sick bed in his horrible lumpen pully, he looked, now how can one put it, to be really rude, to make the cruel remark he himself is the master of, he looked seedy.

Oh dear, that will hurt him. Like most people who dish it out, he's not so keen to receive it.

'I'm beginning to realise that things her enemies have been saying about her have a certain degree of truth. I found it hard to believe for almost the whole of last year that any member of the Royal Family would actually give information to journalists. But now I have to accept that the Princess of Wales has been meeting Andrew Morton in a transport caff and telling him everything . . .'

Hold on, Andrew, who told you that?

'What? Oh, it's true, probably, don't you think? But it was very foolish of her. Oh, if only she had come to me.'

And what would your considered advice have been? 'The Royal Family are not like you and me. They live in houses so big that you can walk round all day and never need to meet your spouse. The Queen and Prince Philip have never shared a bedroom in their lives. They don't even have breakfast together. Diana could easily have done that, and nobody would have known. She knew she was taking on a job as well as a husband, so I would have told her not to throw in the sponge. But we are in deep water here. There are things I still don't understand . . .'

Not that that will hold him back from holding forth. Mr Wilson has always specialised in glorious generalisations, based on the slimmest of information, which is why his journalism is so enjoyable and his biographies so readable. 'But this does happen to be the best royal story since Mrs Simpson.'

He also happens to have just signed a handsome contract with Sinclair-Stevenson for a book called The Fall of the House of Windsor. A German publisher thought of it, and rights are now being sold round the world.

'I believe the collapse of the House of Windsor is tied in with the collapse of the Church of England. Mrs Thatcher must also take a lot of the blame.'

Excuse me? 'The British public subconsciously turned her into their president, an icon with a handbag. The Queen disliked her because she took her place.

'I also have a theory that the Queen herself can be blamed for what has happened. She didn't like the Royal Family being ignored by a major newspaper, so it became a challenge for her to make news, encouraging her children to behave badly, then setting fire to one of her houses, anything to get on the front page of the Independent . . .'

Then he burst out laughing. Is he a tease, Andrew Wilson, or what? While talking, while writing, he believes every word, finding himself swept along by his own theories, then he stops, looks back, and sometimes finds he doesn't believe a word of what he's just said.

He's 42, goodness, is that all, which is what people have said about him for most of his life. His father, one-time managing director of Wedgwood, was 51 when Andrew was born. When he went to his tailor, he bought two suits, one for himself, one for Andrew. Aged 14, young Andrew would sit with his father, in his suit, sipping sherry, discussing articles in the Daily Telegraph. 'We were like two little old men in their club. The Sixties might never have happened, as far as I was concerned. Or the 20th century.'

He broke out once at Rugby, writing an article for the school magazine against public schools, which was picked up by the Daily Express. 'Reporters arrived at the school gates, wanting to interview me, but my house master, wisely, would not let me talk to them.'

He went to New College, Oxford, to read English and was very disappointed to get a second, not a first. He drifted into a seminary, preparing to take holy orders, probably to spite his father, now that he thinks about it, as his father was violently against religion. He left after a year and drifted into teaching in a public school, going home to his wife and family in Oxford at weekends.

He met Katherine Duncan-Jones while in his first year at Oxford - and married her in his second year. She was 10 years older, an English don, though she didn't teach him. They had a church wedding, and produced two daughters pretty quickly. He says he was hopeless as a Dad when they were small, loathed having babies around, didn't help until they were about four.

He then got a job as a lecturer at Oxford. Rather fortunate, considering his degree and lack of research, or was it a fiddle? 'Not quite, but I did have chums who helped. It so happened that two colleges had nobody to teach Old English. I had never studied anything later than Chaucer, so I was suitable, but I didn't enjoy it. I did it for five years, till I was rumbled.

'I suppose if I'd got a brilliant first and done research I might still be a don today, but I hope not. People become dons because they are incapable of doing anything else in life. Twenty years ago, the cleverest people did tend to become dons, but not any more. The really clever people now want to be lawyers or journalists. And more and more the really clever students don't want to go to university anyway. Personally, I think universities are finished. So much rubbish gets taught. I can just see the sort of don I would have become - smug, self-satisfied, living in a fantasty world, playing out a role . . .'

Er, some people might think that is a bit like you.

'Oh no, I'm very self-critical. I may have assumed roles in my time, but not for long. When you live in the real world, two weeks is the limit, before everyone laughs you out of it.'

When he first emerged on the literary scene in the late Seventies, with a sequence of clever, elegant, amusing novels, most of which won prizes, he did appear to be playing a role. The Young Fogey. How real was that?

'I might have been trying on a few attitudes for size, but it wasn't a pose. It was how I'd been brought up. I used to spend hours wondering whether I should rather have been a contemporary of Dr Johnson, or born in 1850 and died just before the First World War. All pointless. We live now, and have to get on with it. But I suppose I'm still a fogey. Over the years, I don't think I've really changed.'

Religiously, he has, from C of E, to Catholic, back to C of E, and now nothing much at all, as he demonstrated last year in his biography of Jesus. 'Even when I believed, I was never steady as a rock. I went from belief to disbelief all the time. I think I became a Catholic to annoy my father.'

In the last 15 years he has produced 23 books, but none has made him a killing, or the large advances now secured by contemporaries such as Julian Barnes, Martin Amis, Ian McEwan or Peter Ackroyd, who have produced far less. Do you go into a sulk when you see their names, the way Virginia Woolf did with Ivy Compton-Burnett?

'There was one person I used to be insanely, irrationally jealous of, and would suffer when I saw his name in print, but you haven't mentioned his name. He has now sunk, rather, so he doesn't bug me any more. The answer is I'm not jealous, nor do I want large advances. I'm proud that no book of mine has failed to earn its advance. I think all advances should be small and authors paid only what they earn.'

I don't believe you. I believe you'd take an obscene advance, if offered, and get the hell out of it, on your bike or otherwise.

'No, with money I fear I would be indolent and bored, which is what happened to my father when he left Wedgwood. Also, I would have missed out on being a journalist. That is exciting. I love having colleagues, instead of sitting alone all day long. I love seeing my opinions instantly in print.'

He fell into popular journalism about five years ago, writing why oh why pieces for the Daily Mail. Now he does a column for the London Evening Standard, where he's also literary editor, a job that takes up three days of his week.

Over the years, he has been rude about a number of eminent literary folk, usually women, such as A S Byatt - saying she looked like a 'blue balloon', Marina Warner 'a bore'. 'Oh, you're not going into all the people I've been horrible about, are you? I haven't much time left.'

No, just to ask why you do it. 'People make the mistake of thinking I do it through malice. I think it's funny. It makes me laugh at the time.' But picking on A S Byatt's appearance, isn't that a bit unfair? 'All right, that was ungallant, but she does take herself so seriously. I think if people enjoy a bit of fame, then the rest of us have a right to be rude. The more rudesbies around, the better.'

What hurts him is any nasty review of his novels, which he does take very seriously. He's just finished one. 'It's about a clergyman who goes off his head. I think it's the best thing I've done.'

Wouldn't it be better to put all his time and energy into novels, rather than ephemeral journalism? 'I think you get energy by expending energy. There's nothing shameful about journalism. Dickens, Thackeray, Dostoevsky, they all worked as journalists. Anyway, I need the money. My father left me nothing.

'I'm a poor little person with a large mortgage. I pay my bills by return and I've never had an overdraft.'

His new wife arrived, bearing a hot drink and dry biscuits for the poor little person in bed, so naturally I asked about her. 'Look, what sort of torrid piece are you writing? Money, religion and sex, that's all you've asked about. On the other hand, I suppose those are the three most important topics.'

His first marriage collapsed after some five years. He is now married to Ruth Guilding, 10 years his junior, whom he met while doing a television series. They live in a tall, thin house in north London. His two daughters visit him, and were in residence that day. Emily is at Balliol, Oxford, doing Greats. Beatrice is reading history at Trinity, Cambridge. Two more dons in the family? 'All I want for them is to be happy.'

His divorce, from all accounts, was pretty painful, and he admits he was selfish to go through with it while the girls were still young, but he is still friends with his first wife.

One of the minor complaints against his writing, either books or articles, is that it is a polished performance, betraying few personal emotions. In the novel just finished, he thinks he does reveal more of himself. And in now writing his House of Windsor book, his own recent divorce should give him insight and understanding.

It will be mostly out of his head, of course. Should he ever meet HRH, she would be foolish to trust him. Remember how he revealed to the world a private dinner party chat with the Queen Mother. But she would find him amusing and stimulating.

In real life, as with many people who can be nasty on paper, he is utterly charming, always courteous, unfailingly kind. Go on, Di, give him a ring. Ask his advice. It would help him over his flu, if nothing else.

(Photograph omitted)