"I'm like a dog in the manger; I don't like the thought of anyone else doing the job," he says in a mock-strop. "I got quite cross when I heard about Emma Thompson adapting Sense and Sensibility. It was absolutely childish of me, but I thought, `I should be doing that. They didn't even ask me. Some mistake, surely. I didn't ask to play the female lead in Howards End. So what's she doing nicking my classic adaptations?'"
As the author of the TV versions of Pride and Prejudice, Middlemarch, Emma, Moll Flanders, House of Cards, Anglo-Saxon Attitudes and The Old Devils, Davies has every right to feel proprietorial. And his pace - he is the Linford Christie of adaptations - shows no sign of slackening. He's still producing scripts at a rate to make even EastEnders writers blanch. Currently, he is in the process of adapting William Thackeray's Vanity Fair, Daniel Deronda by George Eliot, Ian McEwan's A Child in Time, From a View to a Death by Anthony Powell, John Le Carre's Tailor from Panama, and The Count of Monte Cristo, by Alexandre Dumas. Phew.
In his early days as an adapter, Davies was tempted to "improve" on the original plots, until he was warned against it by a particularly expert literary critic. "I got invited to No 10 Downing Street, and John Major said, `you shouldn't have thrown that girl off the roof at the end of House of Cards, you know.' `I'm terribly sorry, sir,' I replied. `I won't do it again.'"
What distinguishes all those works, says Davies, is their universality. "Look at Jane Austen. Her characters derive in a reasonably straight line from fairy tales. Her lead females are like Cinderella and Snow White, endangered women waiting for a prince who is usually fenced off from them by some rich, powerful bitch. They've got the simplicity of the struggle for love and self-realisation, supported by brilliant dialogue and plots like Swiss clocks.
"The primitive appeal is there. Emotionally these writers go very deep without insulting your intelligence. They have got such a grip on the way the world is, that some bloke who never usually watches telly, and spends his days talking on his mobile and boring the shit out of people on trains, comes in, watches a classic adaptation and thinks, `I'm in exactly the same situation as that bloke. I hope he's OK. He shouldn't do that, or the bank will foreclose on him.' The originals can stand a lot of mucking about with by the likes of me."
Even Davies, however, can suffer from a disease more prevalent than gastric flu: perioditis overdosis. We've all sat in front of the telly and thought, "if I see another corset or carriage, I'm going to reach for my revolver."
"I am worried that the bubble may burst," Davies confesses. "I know that a ridiculous number of classic serials have been commissioned, and that reviews show a reaction against them. The critics seem fed up."
So to head them off at the pass, Davies has penned a screenplay which is everything a costume drama isn't. Getting Hurt is a contemporary film about obsessive love, with enough sex and violence to exhaust a censor's supply of red pencils. Imagine a version of the Kama Sutra set in today's Britain, voiced by Graham Taylor, and you're half-way there.
In this stark tale, a respectable lawyer, Charlie (Ciaran Hinds), wrecks his marriage, his career and his sanity on a fatally attractive barmaid called Viola (Amanda Ooms). With his world in tatters, he describes her as someone "just cut out to be one of those that desperate men choose to shatter themselves upon."
Davies reckons that this is a "powerful theme because deep down each of us thinks that we're capable and deserving of absolute and all-consuming love".
He himself admits to having drawn inspiration from a past love-affair: "I suppose almost everything comes from one's personal experience to one degree or another.
"In a way, we go looking for this sort of thing," he continues. "There is this self-destructive urge in people, something perverse in us that's looking out for someone to smash ourselves against. As Viola says in the film, it's like driving your car into the wall. Even at my advanced age [he is 61], it's hard to reconcile yourself to the reality that nothing intense lasts for ever. We like that extra sense of being alive we get from a love-affair. A car crash makes you feel twice as alive - assuming you survive it."
Getting Hurt's overwhelming sense of intensity - much of it graphically portrayed - is Davies's way of revolting against the gentility of the bonnets-and-bustles period. "I had been writing a lot of adaptations of classics, with their finely-woven observations and manners, and I had this strong reaction to them all of a sudden. I thought, `that's not how people are at all.' We are blundering around in the dark in our passionate relationships, and it's a folly and a sham to pretend otherwise. It's only afterwards that things become clear in any way."
Davies also felt constrained by the mores of previous eras. His white hair and thickening body may proclaim late middle age, but his twinkling eyes betray nothing but youthful, flirtatious mischief. He could probably adapt the Solihull Yellow Pages into a TV play quivering with passion.
"I adore doing classic adaptations," he says, "but I also feel their frustrations and their limitations. I've just adapted Vanity Fair. Thackeray, like Dickens, is tremendously bothered by sex, but he can't come out and talk about it. He gives hints that Becky in Vanity Fair is shagging everybody, but if you're going to be faithful to the book, you can't distort it and show that. In all these adaptations, you're trying to nudge the viewer in the right direction in a delicate and subtle way. But if I'm writing the story myself, I can tell it as it is."
Original writing also offers Davies the chance to remind producers that he is just as comfortable dreaming up his own plots, as when hijacking someone else's. "To some people, I'm just a hired hand, an adapter rather than someone expressing himself all over the place. `Go away with your middle-aged lust,' they say, `just tell us how the Count gets his revenge.' But for me, original writing shows that I'm not dead, and that I still get tremors."
`Getting Hurt' is on BBC2 at 10pm on Sunday.