What is it like, that magical moment when the creative juices start to flow? Is it one glorious spurt? Or merely a dutiful grind? The Pet Shop Boys, Neil Tennant

  I prefer Tennant to Lowe - women usually do. He's the tall Pet Shop Boy with luscious eyes who looks as if he only needs the love of a good woman to sort him out. Unfortunately, one gathers from the words of 'Can you forgive her?' that this is an illusion, but still...

Actually, I prefer Neil Tennant because he writes the lyrics, and the lyrics to Pet Shop Boys songs are extraordinarily good. You don't notice them at first, because Chris Lowe's music is so insistent - 'mindless', the way pop music should be. But round about the sixth time you play, say, 'Yesterday when I was mad', you start noticing that it's telling a poignant story very deftly. Tennant wrote it when they came back from their American tour of 1991 and it describes the paranoia that touring induces, and the false friends who make remarks like, 'Darling you were wonderful/You really were quite good.'

When I met him he was in the middle of making the video to go with the song. I didn't meet Chris Lowe because he was 'off being a lightbulb' in New York. This turned out to mean going through some computer scanning wizardry whereby his head could be depicted as a lightbulb. Tennant, meanwhile, was being filmed by more conventional techniques, going mad in the basement of the disused Westminster Hospital. ('We had dozens of disused hospitals to choose from,' he explained, 'thanks to Mrs Bottomley.') He said that the only thing he'd stipulated for the video was that "he" should be the one voicing all the rude remarks in the song. Thus it is he who sings, 'It's fabulous you're still around today/You've both made such a little go a very long way', a point I might well have made in this article if he hadn't made it first. And here, immediately, we are into what is either the weakness or the strength, according to taste, of the PSB - their knowingness, wit, irony, detachment, call it what you will, a cool, controlling intelligence that is somehow at odds with the whole idea of pop music.

Paul McCartney once defined pop as 'innocent talent' but no one is less innocent than Tennant. He claims he doesn't want to be 'ironic', he doesn't want to be praised for his 'deadpan' singing, which seems to mock the sincerity of the words. He says, 'It is obviously a failure of ours, that we have given people the impression that what we do is some kind of elaborate joke.' Nevertheless it is this 'irony' - post-modernist irony, if you want to go the whole hog - that makes it OK to like the Pet Shop Boys. If they were just a boy due singing about their bedsit love affairs we wouldn't want to know.

Tennant claims to want to be simple and to hate pretension, But it is not chance that one of his songs is named after a Trollope novel ("Can You Forgive Her?") of that the video for 'Go West' contains allusions to Pressburger's "A Matter of Life and Death". The writers he admires are Noel Coward and Joe Orton. He says he likes theatre because it is both bourgeois and making fun of the bourgeoisie. And likewise of music, he says, 'We are in pop but not of it.' This is all clever stuff, deeply gratifying to theorists of post- modernism, and segues effortlessly into chat about Andy Warhol and so on.

But another way of putting it is this: the Pet Shop Boys produce music that is simple and catchy and commercial enough to get into the top ten; but the lyrics, videos and imagery are complex and interesting enough to engage an intelligent audience. Chris Lowe's disco beat buys the Boys the freedom to be arty.

In fact, of course, there is something very pretentious indeed about wanting to be 'in pop but not of it'. It is a sort of con trick. I wonder how deliberately it was formulated? Tennant had the huge and unusual advantage of coming into pop from pop journalism - he was assistant editor of "Smash Hits" - so he had seen all the mistakes pop groups usually make with their careers. The PSB make very few mistakes, except their name, which gave EMI directors a heart attack as soon as someone told them about nasty gay-sado practices with hamsters. Since then, in every interview, they have recited like a mantra that they called themselves the PSB because they had some friends who worked in a pet shop.

Reading Tennant's interviews and realising how cannily he had pitched them to specific targets, one knows there is no such thing as an artless conversation with the Boy. Still, he is fun to meet - chatty, gossipy and formidably well informed. We lunched at Odin's and he worried my at first by saying he was on a diet, but it turned out to be the 'Dine Out and Lose Weight' diet which allowed three courses and substantial quantities of champagne, claret and dessert wine. (We reeled out of the restaurant at 4pm.) I reminded him we'd met before, in New York in March 1985, where we were both interviewing a hideously rude singer called Marilyn. Mariella Frostrup, the PR in charge of that junket, told me then that Neil Tennant would soon be famous, but I didn't believe her. Actually, that was probably the last moment when he wasn't famous. The PSB's first single, 'West End Girls', went to number one in Britain and eight other countries within the year. Since then there have been three more number ones, five albums selling 21 million copies altogether, two 'world tours', several extraneous projects such as producing records for Liza Minnelli and Dusty Springfield and the recent 'Ab Fab' single for Comic Relief, and 25 brilliant videos. Altogether a very healthy achievement for a Boy who became a pop singer only when he was almost 30.

And now he's 40! Ooh! Tennant says it doesn't worry him but I bet it does. His birthday was in July and he had a big party. When I tried to get him to discuss the implications of being 40, he said he 'couldn't really think of anything to say, actually.' This was the answer to how he controls his interviews - if he doesn't like the subject, he doesn't discuss it.

He dreamed of being a pop singer from the age of nine, when his parents let him stay up late to watch the Beatles' Royal Variety Performance. 'My sister Susan was in her nightdress and I was in pyjamas, and I remember they had Harry Secombe on before, and you could hear the fans screaming outside, and I felt literally sick with excitement.' He got a guitar for his 12th birthday and started writing songs.

Hating his sport Catholic school, he looked around at the other pupils and thought, 'Well, you're all going to have boring middle-class lives and I'm going to be a superstar!' He always, he said, had delusions of grandeur: in his pubertal religious phase he decided to be Pope. But in the end he did a history degree at a London polytechnic, worked in book publishing and then joined "Smash Hits". He wrote songs all the time but they were, he admits now, 'a bit wet - very singer-songwriterly'.

It was meeting Chris Lowe in 1981 that changed everything. Tennant was a musical snob in those days; Lowe wasn't - he liked "Saturday Night Fever", simple disco melodies with a strong beat and no fancy chord changes. He told Tennant to write fewer words per song, and to make them sexier. Lowe was five years younger and still a student (of architecture), but Tennant recognised that he knew more about music - he'd done music A-level and his grandfather had been in the Nitwits.

It was this unlikely combination of opposites - Tennant with his sad, thoughtful lyrics and Lowe with his jaunty insouciant upbeat music - that made for success. Tennant is quite clear ('without a shadow of doubt') that he could never have made it on his own. He is the Paul McCartney to Chris Lowe's Lennon, the Morecambe to his Wise.

In photographs he often looks like Lowe's custodian, standing stiff to the camera while Lowe slouches or sulks by his side. The age gap is only five years but image-wise it seems more - Lowe is the eternal 'boy' and in interviews Tennant often sounds like his uncle, or keeper. Most of our knowledge of Lowe is derived from Tennant because Lowe doesn't give interviews or, if he does, doesn't talk.

Despite what most people assumed, Tennant and Lowe were never lovers. When they met, in 1981, Tennant was still confused about his sexuality - 'immature in some ways, I think'. He'd had two quite long relationships with women in the Seventies, finally decided he was gay in the early Eighties and responded by being celibate for most of the decade, partly through fear of Aids, partly through insecurity. He never liked casual sex, and still doesn't: 'I'm rather romantic, really. People nowadays present sex as a sort of sport, a healthy leisure activity like jogging, and I can't really see it like that - I think it's more complicated, actually.'

He wants meaningful, lasting relationships, and he wants fidelity. He is very scornful of a remark of Edmund White's that his lover was 'generous with his body' - he wants none of that malarkey. In an interview he gave very early in his career, he said that most of his relationships ended after three years because he was so possessive. He says now that he was 'talking bollocks' (i.e. wishes he hadn't given that interview), but concedes that three years is still his record. In fact, one three-year relationship ended earlier this year and he was so seriously depressed he thought of going to a therapist.

It is surprising that Tennant is telling me all this, because for years he never talked about his love life. He told the "New Musical Express" in 1986, 'We've never said anything about our sex lives to the newspapers or to magazines. And we don't intend to.' Though many of their songs were on gay themes, though they supported Aids causes and sang at an anti-Clause 28 benefit, they never actually 'came out' - and were attacked by gay activists for what was seen as their cowardice. Tennant now explains, 'One of the reasons I don't like to be classified totally as being gay - and I'd be happier to say homosexual - is that is carries so much baggage. There are all these cultural assumptions and I don't really care for them. I also think the idea of "gay" is slightly old- fashioned now, because it was a civil rights response to define oneself so strongly and separately. But I don't like separatism, or ghettos, of any kind. I think if you split up into little interest groups, it destroys society and I'm very much in favour of society.'

This speech has a slight feeling of being rehearsed. In any case, it doesn't really explain why he is willing to say he is gay now, when he wasn't eight years ago. Could it be the effect of turning 40? Cynics might say it was because the PSB's marketing position has changed. But I would guess it was because he was never 'glad to be gay'. He was, in fact, rather reluctant, given his good Catholic family background and his distaste for promiscuity. One of his lyrics declares bluntly, 'It's a sin.'

Although Tennant is always relentlessly 'up' in his interviews, you sense a great capacity for depression, and possibly maudlin self-pity, when he's alone. It is remarkable when, once, he lets it show: the Newcastle accent becomes much stronger, and he stops talking at his normal 100 words per minute and drops down to about three words and long silences. It happened when I asked what was the kindest thing Chris Lowe had ever done for him. His face crumpled: I thought he might cry. Finally he mumbled that Chris was kind when his lover left him earlier this year - he invited him to stay. He looked tearful again when talking about the three friends he has lost to Aids in the past year - Derek Jarman, who designed the PSB's first stage show; an old school-friend from Newcastle and Peter Andreas, who lived with Lowe for five years and died in March. As he sings on 'Very', 'There are no more lovers left alive/No one has survived.'

What would have happened to him if he had not met Lowe? He says he'd still be in pop journalism: 'I'd probably be managing editor of Q magazine by now.' It is significant that he says managing editor rather than editor - the managing editor is the one who handles the business side. Tennant obviously understands money (when he worked in publishing, he was chosen by his colleagues to negotiate on their behalf with Robert Maxwell) and he has made some very cool decisions. Right at the beginning, he went to New York and signed up with the producer Bobby Orlando, but he spent the proceeds of their first hit, 'West End Girls', buying them out of their contract. It cost a million dollars and they remained hard-up, living in grotty one-room flats for two or three years after they were famous. But, in the long term, it was a shrewd decision. Tennant admits he is meaner than Lowe - which probably means he is better at handling money. He was pleased that I paid for our lunch.

He confesses that he and Lowe spend a lot of time wondering why they aren't richer than they are. They have sold a total of 21 million albums, of which their cut is about £1 an album, so in theory they've made £21 million but, wails Tennant, 'Where is it? I don't think even now we're mega-rich - we're only worth a couple of million each.' Pop money, of course, is always shrouded in a great cloud of unknowing, compounded by ignorance on the part of the press and wilful exaggeration by PRs, but even Tennant is mystified. He says their last album, Very, cost about £1 million to make, comprising £300,000 recording costs, five promo videos at £70,000 each, ten remixes for the clubs at about £5,000 each, then odds and ends like photographs, costumes and design. So only after it has sold a million do they start to show a profit. They control everything themselves, from choosing the songs to hiring video directors and designing their packaging.

'For me, being in the Pet Shop Boys has always been a struggle between total embarrassment and total shamelessness,' Tennant says. Will embarrassment prevail now he has turned 40? He sounds quite hazy about the future; he says there is nothing in his diary after next week's release of an album of remixes called Disco 2. It will include their recent 'Ab Fab' record, though Tennant grimaces when I mention it. The pop press hated it - a 'novelty record' (sneer) and for charity (double sneer with knobs on). In a recent interview with NME, Tennant said the article was bound to say, 'The single is awful, we're too old and our career is finished.' The article ended by saying precisely that - and without the grace of quotation marks.

But the Pet Shop Boys have now moved beyond the need for pop press approval. They have a surprisingly heterogeneous audience, ranging through many ages and levels of sophistication. Tennant in inured to the fact that pretty boys in clubs come up and tell him, 'My Mum really likes you.' He also says with some surprise that the video of 'Go West' was a huge hit with the under-tens. Thus, while they have probably lost some of their street cred in recent years, they have picked up new fans, mainly through their consistently brilliant videos.

Their career is so improbable anyway that it can't be judged by any pop norms. The only other singer I can think of who has achieved so much on the basis of such limited singing talent is Madonna, and she's done all right. In the song 'Being Boring' - which he admits is autobiographical - Tennant sings, 'I never dreamt that I would get to be/The creature that I always meant to be.' He says they only really ever had one big ambition - to get a record produced by Bobby O and released on import so it could be sold in Soho's Record Shack. They achieved that in April 1984 and everything since has been icing on the cake. Nice icing.