The warm chuckles around the biscuit barrel come from Dad's Army star Bill Pertwee, clad from shoulder to shoe in tweed, and from Burt Kwouk, of karate-kicking Pink Panther fame. The two veterans are whiling away the time between takes by chatting with Hill's director, Robin Nash, a man who is himself a national treasure, with a kitsch television provenance taking in Dixon of Dock Green and The Generation Game.
"All the songs that Harry sang with Burt in the last series went down very well," the producer, Charlie Hanson, confides in me, as Kwouk is called into a recording studio to put on his headphones and join Hill in a rendition of a current rap hit. "So we have decided to do a few more."
In truth, the whole series went down very well last time, winning a creditable 2.5 million viewers and industry awards left, right and centre. It also earned Hill his moment with the frequently-slapped-about title of Britain's best new comedian.
So I wonder, as I listen to chit-chat in the lobby about which aged Equity member has died most recently, what makes a hot young entertainer surround himself with such comfy old retainers. Fortunately, it is a nostalgic trend that fits in neatly with Hill's post-modern passion for the incongruous. And what could possibly be more incongruous, after all, than listening to Burt Kwouk rapping out urban discontent. Unless, of course, it would be to hear Little and Large sing the hits of the Pet Shop Boys (and they have already done that for the first show of the new series).
When Hill eventually emerges, flushed from his rap session, he looks as if he is going to confirm his rather embarrassing reputation as the "nicest man in the business". In a moderate check shirt, jeans and a pair of glasses that bear only a muted resemblance to those he wears on stage, he diffidently explains how he chooses the songs for the show.
"I list all the ones I would like permission to do and then it whittles down. The Beatles never say 'yes'," he complains. Hill is also miffed by Jeff Lynn's recent decision not to let him perform "Xanadu". "I thought that would have been a great finale," he says.
Each of the TV shows is based around a series of wilfully silly monologues from Hill. Then, notwithstanding interruptions from a troupe of badgers and from a blue, streetwise glove puppet called Stouffer the Cat, the half-hour builds to a grand finale in which the comic is joined by all his guests for a song and dance number. It's a time-honoured tradition which Hill happily concedes owes just as much to Crackerjack as to Morecambe and Wise.
"I got out a video of Crackerjack the other day and I had forgotten how long their finales were. We are quite pushed for time in comparison."
For those not yet inducted into Harry Hill's strange world, he is a former doctor from the home counties who gave up medicine to become a highly successful absurdist comedian. In the last five years he has almost single- handedly subverted the observationist strain that was running through British stand-up routines. Comedy fans who had grown tired of pedestrian gags which all began with a question like, "Have you ever noticed how your girlfriend always puts the loo seat down?", have grabbed Hill's pacy surrealism with both hands and not yet put it down.
Typical Hill observations run along less well-travelled lines: "Wouldn't it be nice," he asks in one show, "when you are doing a brass rubbing, wouldn't it be nice, if just for once it didn't turn out to be a knight?"
Clever, yet entirely unthreatening, he has a genuine cult following among lots of young lads and is afforded the same kind of reverence as The Goons and Monty Python were in their day. (Last summer the magazine Loaded ditched its scantily dressed cover girl in order to picture Hill sitting racily astride a giant badger).
He first came to national attention in 1992 when he won the Perrier Best Newcomer's Award at the Edinburgh Fringe, and in 1994 he went on to produce a series of weird, slapstick films called Fruit Fancies for BBC2. The first series of Channel 4's Harry Hill won a British Comedy Award last year and a video of his acclaimed show at The Palladium comes out next month.
Perhaps the most unlikely feather in his cap, metaphorically speaking (you have to make these things clear in Hill's case), is his run of appearances on David Letterman in the US. He was the first British comedian to perform on the show and he has already been back twice.
"In many ways, Letterman was easier to do than something like Des O'Connor over here," says Hill. "With Des, you know that all the other comedians you know are watching. But with America that's not true, and you have also got all the excuses ready for you if it doesn't work."
The act had to be altered for an American audience and Hill prepared on each occasion with a week of stand-up gigs in New York.
"I had a really hard time in some of those places. Died on my ass. You forget how difficult the accent is for them. Obviously you have to say elevator instead of lift, but they don't know what a KitKat or a badger is over there. And all the American comics come out and talk to the audience for a while, whereas British comics, like me, start with a joke straight away. They are not expecting that."
My observation that friendly banter with the audience is a bit too sensible for Hill's stage persona goes down badly. He does not like to be legislated for and says he may now have to look into a way of making it work.
Hill, whose real name is Matthew Hall, finds it hard to say what drew him to comedy. He knows he gets bored easily, and that the job of a comedian is more fun than anything else he has done, but it has never been a form of rebellion for him. Although he was one of a gang of sarcastic smart- alecs at school in Staplehurst, Kent, he claims he always wanted his humour to be inclusive and that he still does not like it when people can't see what he is getting at.
"Most of my jokes are as plain as the nose on your face. I am not trying to trick the audience," he says. "The only mischievous thing I used to do was that, if I was going down badly in a club, I would dig myself in further deliberately. I would never compromise. I didn't want to be pushed around."
If this sounds tough, one should remember that Hill's routines contain no swearing whatsoever and consist, in the main, of non-sequiturs followed by daft suggestions; for example, that all short people should wear numbers - not just jockeys.
"I have found it difficult in clubs where I have gone on after a comic who has done a lot of knob jokes. It can be hard for me with an act that is this... stupid, or quirky, or whatever you want to call it."
His act and his brand of naive humour, both have their roots in the medical student revues he co-wrote while he studied at St George's Hospital in Tooting. He was not at any time, however, and Hill is emphatic on this point, one of those medical students that you see running around with shopping trolleys during rag week. "You were either revue or rag week," he says "I used to write loads of terrible sketches. I had to be so straight most of the time that I just liked seeing if I could get away with it."
He regularly visited comedy clubs and admired the "deadpan, sharp-witted types" like Arnold Brown, Norman Lovett and Arthur Smith. "I can remember going up to Jack Dee and saying, 'I think you are marvellous'."
Hill tried out as a double-act at first, but his solo set, with his trademark high collar and pocket full of pens, did not appear until he started working with Al Murray at The Kings Head in Islington and turned his back forever on a medical career. "As a boy, I had a romantic idea about becoming a brain surgeon, but even back at Tooting I was secretly thinking, 'What the hell am I going to do?' Once I was committed to comedy, suddenly I fitted in. I was finding people that had the same interests, jokes. At Tooting they really were a middle-class, square bunch."
But at 34, and now the father of two baby girls, Hill himself is no longer up to painting the town red. "I used to hang around and have a drink with the other comedians, but I am quite anti-social now," he says, although he denies the implication that he has fallen into the easy life of an established celebrity. "People think if you have made a name for yourself, it is all sorted out. It is not like that. Expectations are much higher, although, of course, you don't have to go out every night to earn a living."
But there are moments of self-congratulation. Hill confesses he felt a certain pride when he was invited back on to David Letterman. What were the chances of that happening, eh? But a cautionary tale follows.
"Before the show they warned me Letterman might come over and chat, so we rehearsed some jokes and in the end he actually called me over to sit with him. Then, during the commercial break, he turned to me and asked if I worked mainly here or in Europe. He obviously had no idea about me. Next, he asked if I had had a good Christmas. I said 'yes' and asked him if I could have a signed photo for a friend. At this point a man appeared at my elbow saying, 'Hi, David has to concentrate on the next part of the show now, so I am here to talk to you'. I can't help thinking Letterman had a panic button hidden somewhere.
"To my friends watching, of course, it would have looked great. But you see, you never really get there."
IN HIS OWN WORDS
On American audiences
'I had a really hard time in some of those places. Died on my ass. You forget how difficult the accent is for them. Obviously you have to say elevator instead of lift, but they don't know what a KitKat or a badger is over there'
On his brand of humour
'Most of my jokes are as plain as the nose on your face. I'm not trying to trick the audience. I have found it difficult in clubs where I have gone on after a comic who has done a lot of knob jokes. It can be hard for me with an act this... stupid, or quirky, or whatever you want to call it'
On not becoming a doctor
'As a boy, I had a romantic idea about becoming a brain surgeon, but once I was committed to comedy, suddenly I fitted in. I was finding people that had the same interests, jokes. At [St George's Hospital] Tooting they really were a middle-class, square bunch'
On being a famous comedian
'People think if you have made a name for yourself, it is all sorted out. It is not like that. Expectations are much higher, although, of course, you don't have to go out every night to earn a living'