Andy Hamilton has strong views on comedy, and on drama. Now the writer of Drop the Dead Donkey has combined the two in his new series, Underworld

"And now a comedy-drama..." These words from continuity announcers have invariably led to a massive surge in demand on the National Grid as viewers dash out to switch on their kettles. Traditionally, the genre has had all the allure of two days bonding in Eastbourne with a group of Tory MPs in bad knitwear.

Sure, there have been honourable exceptions - Auf Wiedersehen Pet, Minder, Preston Front - but generally, comedy-dramas have crashed and burned because, well, they're neither comedies not dramas.

Andy Hamilton, progenitor of Underworld, the latest attempt to rehabilitate the genre, admits that it is in sore need of an image makeover. "Comedy- drama has mistakenly become a synonym for soft, safe drama," he admits. "There's too much of it about, and it gets spread a bit thin."

He hopes Underworld might help change that perception. It is certainly a gripping story; it centres on William and Susan, a decent brother and sister (convincingly brought to life by James Fleet and Susan Wooldridge) plunged way out their depth into a world of gangland violence. Despite that grim summary, the writer has seamlessly woven many moments of light into the darkness. You laugh as you wince when William is punched by a villain on his doorstep posing as a Lib Dem canvassing his views on law and order. Hamilton's knack is skilfully to intermingle humour and hardness.

Understandably, then, Hamilton is reluctant to tar Underworld with the conventional comedy-drama brush. "We tried to create a composite noun for it - something like `dramedy', which the Americans have coined. But all we could come up with was `blacomthrillama' - black comedy thriller drama - because it's all those things simultaneously. On one level, it's good that it's not easy to describe, but it does make it hard to market."

As regular listeners to Radio 4's News Quiz will know, Hamilton positively buzzes with ideas. "I think of Underworld as drama where funny and serious things can happen simultaneously - as they do in real life," he muses. "There's no need to demarcate them in the way that some drama does. Sometimes, drama doesn't include anything funny in case it undermines the seriousness of the piece. But thanks to people like Jimmy McGovern, a comic moment can actually be more touching than a serious one.

"Look at the way William lies to Susan about her ex-husband," he continues. "It's comic because we can see it's going to go horribly wrong, but at the same time it's touching because he's a man who hates rows. So it's a comic device which illustrates a familiar trait in a lot of English people."

Hamilton made his name as a purveyor of bespoke sitcoms of quality to the networks (Shelley, Drop the Dead Donkey), but does not perceive a mighty chasm between there and the world of drama. "I don't see it as a big leap," he maintains. "David Renwick [who made a similar move from sitcom, One Foot in the Grave, to drama, Jonathan Creek, earlier this year] would give you the same answer. I've always seen sitcom as just another form of dramatic storytelling - it's merely in a different register."

Supping a pint in a north London pub after a hard day fine-tuning Underworld, the writer reckons he is flexing the same muscles whatever he's working on. "Drama uses the same story-telling techniques as sitcom - it's just a bigger canvas," he argues. "The fundamental questions are the same - Do I believe the characters' motivations? Do we need to change the rhythm of the piece?"

More than most, Hamilton is well-practised in defending sitcoms. "There's a certain fashionable snobbery," he sighs. "The `What's wrong with the British sitcom' article comes out every other Thursday in the broadsheets, usually written by a food critic. They always hold up American comedies as the great benchmark, forgetting that we only see the best of them."

The reputation of sitcoms has suffered, he contends, because "broadcasters don't treat them seriously enough. A lot of television executives think that the best sitcoms happen up at the frothy, lighter end of the market.

To emphasise that comedy can handle serious subjects, Hamilton recalls a seminar on Drop the Dead Donkey he attended in Denmark. "A local producer stood up and listed the topics covered in the sitcom," he remembers. "He said: `1. Death. 2. Fear of death. 3. Addiction. 4. Nymphomania. 5. Professional Betrayal.' These are all very disturbing subjects. You realise that's the currency the series draws on. Only syphilis and incest weren't on the list."

`Underworld' begins on 4 Nov at 10pm on C4