At five o'clock, there Jenkin was, well over six foot, topped by a hewn crop of densely curlicued hair, with a look smeared across his face as if he's permanently attempting to suppress a back-of-the-class snigger. Thanks to a crossed wire, he wasn't alone. Up pitched Andy Hamilton, his shorter, rounder, and black-bearded scriptwriting other half. The interviewer's manual on etiquette is no help here: there are precious few guidelines on how to turf out gatecrashers without causing offence. Thank God for Drop the Dead Donkey, the latest fruit of their long partnership which, coincidentally, makes its latest appearance in the same week as Crossing the Floor. A furtive reordering of the questions, and it was perfectly possible to divert some of the inquiries intended for Jenkin through to Hamilton. In the end, Hamilton probably ended up talking more.
They may look as different as a pair of comically mismatched cartoon criminals, but we can take Hamilton's unbidden appearance as evidence that they emerged joined at the hip from the same womb. They certainly sound as if they did, intuitively butting in, mid-syllable, on each other's answers. Take an innocent question about the difficulty of reconvening the cast of Drop the Dead Donkey, at least the two (Stephen Tompkinson and Neil Pearson) whom the show has transformed into stars. Hamilton: "They've just signed up because they want to do it. It's nice to know that ..." Jenkin: "...fifty shows down the road ..." Hamilton: "... you're still able to attract the same lot back."
It's actually something of a myth that they are forever in collaboration. Both directors of the recently formed Hat Trick Films, they see each other to talk about their own and each other's projects (Hamilton has one script on the slate and Jenkin three). But they are a far less constant script team than Marks and Gran or Clement and La Frenais. They journeyed more or less together along the traditional staging posts of clever-clever comedy writing - Cambridge, Week Ending, Not the Nine O'Clock News and Spitting Image. "But we were never Siamese twins," says Jenkin. "We've written for a lot of the same programmes but we weren't a writing team."
"We've always been an open marriage," adds Hamilton. "We've always been fairly promiscuous and gone off and worked with other people."
It would be easy to line up their solo scripts and conclude that they are going their separate ways. The most recent fruit of Hamilton's wanderlust was Eleven Men Against Eleven, a hilarious conflation into one script of football's annus scandalus. Jenkin's equivalent piece of rapid-response drama was A Very Open Prison, which turned the travails of Home Secretary David Hanratty into similarly high-octane comedy. Since then there's been nothing else from Hamilton but two more single dramas from Jenkin - first, The Lord of Misrule, in which a dyspeptic Lord Chancellor holds the Tory government to ransom by threatening to flog his memoirs, and now Crossing the Floor, in which Hanratty expedites an election by joining a new, ultrabrite Labour.
It's easy to detect a gathering darkness in Jenkin's work. Just as it was a large but logical step for Alan Ayckbourn to write his first corpse into a play, something similar has happened to Jenkin, who perhaps uncoincidentally shares the Swan of Scarborough's speed out of the blocks. But if Hamilton would not yet seem to have gone down that route, it may be simply for practical reasons. He has three children to Jenkin's none, and that "Might have put a little bit of a dent in my step," he says.
"Our speeds have probably separated a bit. Guy is probably as fast as he ever was, and I think I have slowed up."
In fact, Hamilton has written a six-part series for Channel 4, to be broadcast next year, called Underworld, which sounds like he's progressing slowly along the profession's well-trodden path into the heart of sun- dappled darkness. "It's about an estranged brother and sister and the survival of decency." He's possibly in denial about the seriousness of it all, as he adds a disclaimer: "Don't put `the survival of decency' in, that'll sound too poncy."
And, anyway, it's not certain that Jenkin has got where he means to go yet. His take on the modern political process is wonderfully cynical and clear-sighted, but he has plainly no such easy route into the private lives of his characters. When the death is announced in Crossing the Floor, that it gets even close to credibility is down to the acuity of Tom Wilkinson's performance as Hanratty rather than what must have looked crudely drastic on the page. Jenkin defends the stark interleaving of light and shade: "Without being too pat about it, life is funny and serious at the same time. I'd like to try to do dramas where the comedy is still very funny but the darkness is genuinely ferocious at points." Still, if Labour win and Hanratty is given a job by his new boss Tom Peel (Neil Pearson at his most blue-eyed), the archaeological dig into the soul of the character can go on.
For the next few weeks, Hamilton and Jenkin are back collaborating on Drop the Dead Donkey, interpolating the topical gags that were the show's original raison d'etre. More up-to-the-minute than ever, a tailpiece will be filmed on the day of transmission. But the series' move from Thursday to Tuesday has forced them, says Hamilton, "to concentrate on the kind of issues that are going to rumble all the way through, like BSE and gun laws", as opposed to their old tendency to "react slightly neurotically to what was in the headlines that morning".
And even Donkey's structurally shallow characters are achieving moderate depth. Dave, the gambling womaniser played by Pearson, will spend the series worrying if he's brave enough to settle down. Gus, the office manager, is trespassing ever closer to the realm of tragedy. We've already had a glimpse of the sheer emptiness of his private life. Now, says Hamilton, "we see that he's got a suppressed fear of mental illness. He's a socially tragic figure, because he's like a casualty of the Eighties. He jumped on board the bandwagon and now worries that it's screaming off into the distance and he's been left behind."
The media supremo in Crossing the Floor is a more demonic figure, a gay- basher by day and a gay clubber by night. He's played, as he was in The Lord of Misrule, by Hamilton. Thanks to the fact that the two shows have been scheduled for the same week, it suddenly occurs to them that there ought to be some form of cross-channel referencing.
"We might have to slag off Crossing the Floor in show two of Drop the Dead Donkey, Guy. `Did you see that thing on Saturday. Oh dear,' " says Hamilton.
" `That bloke who played the editor was crap. Wasn't he?' " adds Jenkin.
"That would be reflexivity gone mad," says Hamilton.
n The new series of `Drop the Dead Donkey' begins tonight at 10pm, Channel 4; `Crossing the Floor' is on Saturday at 9.30pm, BBC2