But inside, heresy of heresies, the frenetically cheerful Chris Evans is getting testy during the commercial break. 'The cables in the hall are a nightmare . . . this is not what I asked for.' For a moment the crew look as if they may burst into tears. Eighty per cent of them, after all, can be no more than 24. But no time to worry. Commercial break over. 'We're in such a good mood today,' Chris announces to the viewers, and it's sunny again.
Upstairs, things are less hunky dory. The actress Nichola McAuliffe has been waiting to be interviewed in Paula Yates's boudoir, but Paula has had a heavy night and doesn't arrive until the last second. The interview is delightfully double edged. 'I'm sorry you've had to wait on the bed for two-and-a-half hours,' grins Paula. 'And I'm sorry you couldn't get out of yours,' beams Nichola.
Just to follow the crew around you have to be fit; moving from lounge to kitchen to boudoir for the next celebrity interview, joke, quiz or any bit of inspired nonsense. Even Peter Smith, the newsreader, takes his jacket off for bulletins.
But as Chris looks intense and pores over cue cards during the next commercial break, from the kitchen comes a peal of infectious laughter, and a shriek: 'Oh, I've just got a kiss.' One of the guest family of the day has just planted a smacker on co-presenter Gaby Roslin. Five minutes earlier she had tears in her eyes as the family's unmarried dad proposed to his partner live on air.
Enter a true child of television. And something of a rarity among media folk, a nice girl. Unlike Mr Evans, Miss Roslin never looks unhappy. But then life is as happy, colourful, profitable and meticulously chaotic as The Big Breakfast itself for this 29-year-old.
Last month at the British Comedy Awards Chris Evans startled her and the audience by calling her up to hand his award to her; The Big Breakfast producers, Planet 24, and Channel 4 are talking to her about spreading her wings; her boyfriend, Colin Peel, a musician with the Praying Mantises, was an understudy in the West End revival of Hair and ended up playing the lead 16 times. And, most of all, she's doing a job for which she's prepared herself from a very early age. 'What would you be doing if you weren't a TV presenter?' I ask her afterwards. 'I would be wanting to be a TV presenter,' she replies instantly. 'I wanted to be a TV presenter from the age of three.'
Her father, Clive Roslin, then a BBC announcer, now a Radio 4 newsreader, took her to watch Blue Peter being made. 'That was a formative experience. I idolised Valerie Singleton. When we got home my parents would pretend they were the cameras. I would be Val.'
School at the progressive King Alfred in Hampstead was followed by a drama course in Guildford and a memorable interview with a teacher. 'We were all asked what our 'flight plan' was. The first student said the RSC, the next the National Theatre, the next said he wanted to do theatre in education. Then I said I wanted to do telly. The teacher asked me what, and I said Blue Peter or the Multi-coloured Swap Shop. She said 'Yes dear', asked to see me afterwards and then demanded: 'What are you doing here?' 'But drama school was good training for a TV presenter, how to hold yourself, how to breathe.'
Ironically, what makes Gaby unusual is her untutored style. She exudes a real enthusiasm and is increasingly used for the more serious, if brief, interview, in which she proves a good listener.
'My father instilled certain values in me,' she says. 'He always said 'For God's sake, listen'. On a lot of TV shows, people forget that. I admire the old ways in broadcasting. It would be conceited for us to say our way is best. There are wonderful interviewers on TV, Aspel, Oprah, even Jonathan Ross.'
After drama school, Gaby took a job on Superchannel's children's programme, Hippo. It was 'a great learning experience; I was presenter, researcher, letter opener', then progressed to Motormouth on ITV before auditioning for The Big Breakfast as co-presenter.
Whether she has emulated her role model, Val Singleton, and become one of the few female presenters to have graduated from children's to adult TV depends on whom you believe about the age range of The Big Breakfast audience. She is adamant that it includes all ages, a view that seems to be borne out by the number of adults who stop her in the street to tell her their problems. Brought up to be scrupulously polite, she always listens, but is shocked that some of those adults turn out to be 'men who are not gentlemen who want to kiss me'. And it is a bit of a shock, almost like goosing Heidi. Although Gaby is tall, blond and pretty, she is not a sex symbol. One newspaper described her as 'every child's big sister'. The persona is sister or daughter, never vamp.
But can that amount of jollity be natural on someone who gets up before 4am every working day? 'Well,' she answers with typical honesty, 'there can be all sorts of reasons why you're not at your best. There's everything from PMT, which can make you not smile. But we do enjoy the job tremendously.'
What was the persona that Planet 24 asked you to put across? 'This is embarrassing. What you see is what you get. There's no persona. It's me. Happy. The word lucky fills my day every five seconds. I enjoy life. I'm shy, believe it or not, but not in a huge way. I like things to be nice and right.' The world can be one long Blue Peter it seems.
Back on the show they're reading out viewers' worst-ever Christmas presents. One woman's mother bought her three-year-old granddaughter a 100-piece jigsaw. It's not that funny, but Gaby bursts out laughing. Happy, enthusiastic, untaxing television is in the care of a lady born to it.