Last script for the doctor

Anyone who has read his book, The Writer's Tale, which tells the inside story of the making of series four, will know that Davies is a man whose tear ducts get plenty of exercise. But ending his tenure on Doctor Who came without recourse to a hankie. "I'm absolutely unsentimental about this sort of thing," he says, talking in his Cardiff flat. "I would have thought that when I handed in the last script I might have burst into tears or got drunk or partied with 20 naked men, but when these great moments happen you find that real life just carries on. The emotion goes into the scripts.

"That's why I do the job. I find the emotional scenes emotional, the exciting scenes exciting. I laugh at the funny stuff and cry at the sad stuff. If you had a camera on me, sitting here at this computer, it would be like Diary Of A Nutter. They could show it on BBC3."

Davies is 45, six feet six, loud, expressive and funny. Possibly because he's gay, it's never written in profiles that he is quite the alpha male. Yes, he suffers from midnight moments of doubt, but essentially he's supremely confident in his talent, and the facts bear out that self-belief. His vision of Doctor Who as a soapy, poppy, flashy and yet, crucially, heartfelt drama has paid off with audiences in excess of 13 million and the complete annexing of the British mainstream.

It has also led to some interesting offers, such as Davies being invited to take part in Dancing On Ice. He declined. "But just after (Boyzone's] Stephen Gately had been on it, I met him and he said, 'Feel my arse.' So I did. It was so hard it was like holding a skull. And then he said, 'That's what ice skating does for you.' So there is something to be said for it."

There will be four special hour-long episodes of Doctor Who broadcast this year, starting this Saturday with Planet Of The Dead. The final two episodes will be broadcast over the Christmas period and conclude with David Tennant's regeneration into Matt Smith, at which point Scottish writer Steven Moffat will take over as executive producer for a new series in 2010.

"The church bells ring when Steven hands in just one of his scripts, so I think a whole series is going to be glorious," says Davies. "We agree on so many other things, but he's not going to come in and copy me. I have read his first episode and it's phenomenal. There are such good times ahead."

Although Doctor Who under Davies has been exciting and funny, there has often been a base note of sadness, specifically to do with characters being separated from one another. He acknowledges that his feelings about the death of his mother in 2002 may have found their way into the work; it's not an experience one can address directly in art, he believes, but the emotions leak on to the page. "The day you lose your mother is one of the saddest days on planet earth," he says, "and one of the saddest things is there's almost nothing to be said about it."

Davies, it seems to me, is your classic sad clown – jokey on the surface, sombre underneath. His Doctor is forever giving speeches about how wonderful humans are, but Davies's own world view is more cynical. In the episode Midnight, passengers trapped inside a vehicle with a malevolent demon of an alien turn against each other and the Doctor in a bid to save their own lives. That's how Davies sees life. But he feels he shouldn't articulate such pessimism too often in a show watched by young people.

There is, however, no separating Davies from his writing. It's how he defines himself, and the aspect of his life on which his self-esteem is based. "To me. It's not a job, it's not work, I wouldn't even call it a vocation, it's simply the way that I think, all day, every day."

On occasion, he has written directly from his own experience. Queer As Folk, which was being broadcast on Channel 4 a decade ago, was a distillation of 15 years on the gay clubbing scene in Manchester between the start of his twenties until his mid-thirties. "I'd be out until five in the morning, get into work at Granada at nine, throw up in the toilets, then go and be brilliant at my job," he wrote in The Writer's Tale.

It was a period of a sometimes dangerous hedonism – and an overdose, which he'd rather not go into in any detail for fear of a My Drugs Hell headline – which ended up being dramatised in Queer As Folk. Was that series a fond farewell to his pleasure-seeking, self-destructive self? "I suppose it was. I didn't realise it at the time, and it didn't coincide so neatly because I carried on for a few years after that, but at 35 it was only a matter of time before they closed the club door on me and said, 'Get out, grandad.' And I got my lovely boyfriend just before I started writing Queer As Folk, so everything fell into the right place really. I suppose writing it did me some good. It's all therapy in the end."

The "lovely boyfriend" is Andrew Smith, a Customs officer. They have been a couple for 11 years but don't live together as Davies believes he would probably kill anyone with whom he shared a home. "Bless him, he's the one sane man in the whole world and is mildly disinterested in Doctor Who. And that's nice. I see him in Manchester and he says, 'How was work?' and I say, 'Fine'. He's beautifully stable, so a good counterpart for me."

Davies writes in Cardiff, through the night, head full of jokes, lungs full of smoke. "Sometimes the creative act is actually quite a sexy process," he says. "When it's working, when it's on fire. You can fancy your characters, you can hate your characters. Writing has an obsessive, unstoppable quality in the same way that sometimes men are terrible monsters driven by lust."

He believes his homosexuality had one significant influence on his writing – it made him an astute observer of behaviour.

"Nowadays there are kids who are confident enough to come out at school, but that didn't exist when I was at school. So during those teenage years when everyone else is snogging and copping off at parties and you're not, you spend a lot of time watching what's going on. I think that watchfulness you develop when you're in the closet does have an effect, but it's not what creates the impetus to write in the first place."

His love of stories goes back to being a child. Growing up in Swansea, the son of two classics teachers, he loved poring over an encyclopedia of Greek and Roman myths. Then there was his mother's collection of Agatha Christie paperbacks, and his own beloved stash of Asterix and Peanuts books. Even now, he can hear the rhythm of Charles Schulz's punchlines in his own writing.

The big question now is what will Davies do next? He has a number of possible TV projects, including one codenamed in his head as More Gay Men. He thinks, too, there's a good chance he will go to America and work in TV there for a while. And he adds: "I do think that one day when I'm 65, if Granada would kindly open their doors, I might have a very happy retirement working on Coronation Street."

So would he be content if, in time, all his other work was forgotten and only Doctor Who was remembered? "No!"

Not that he really cares about posterity. A resolute atheist who once cast Richard Dawkins in Doctor Who, he has no belief in the afterlife, so doesn't believe he'll be "looking down, beaming" as repeats of Queer As Folk are shown on UK Gold.

"And frankly," he laughs, "in 50 years' time we'll all be foraging through the wilderness like wild dogs. So what the f*** does it matter what's going to be on television?" v

Doctor Who: Planet Of The Dead is on BBC1, April 11, 6.45pm