Michael Parkinson: The smoothest of all operators

"Dat-diddly-da-da-da!" It's three hours before showtime, and the Parkinson theme tune fills the cavernous arena of ITV's Studio 1 as the pianist Laurie Holloway conducts the last Big Band working in British television.

Parky himself is already in the house but not yet on the set as Holloway and his fellow-musicians rehearse. The room is drenched in blue light but the audience seats are empty, save for one man taking a snooze in spite of the clashing cymbals. There's just time to walk the famous walk.

Directly behind the Parkinson stage is a little box-room, with no ceiling and four walls made from thin board covered in blue felt and decorated with photos of Michael Parkinson with such stellar guests as Dame Judi Dench, Renée Zellweger, Rod Stewart and Tina Turner. This small space is furnished with two leather sofas, a glass table with some bottles of Aqua-Pura, and a TV monitor with a sign saying, "Do not place drinks here!"

From this "room", tonight's invitees - Gene Wilder, Patrick Stewart and Ian Hislop - will follow on the path of Parkinson himself, ascending 11 blue-carpeted steps, pausing momentarily on a small landing and, taking their cue from another small monitor, making the final curved descent of eight stairs to orchestral fanfare and the applause of more than 500 studio guests.

Parkinson will tonight make this journey for the 576th time in a career that has established him as Britain's king of the chat show. "I've never lost the wonder at it all," he says. "I love walking down those stairs. There's nothing like it, a big band blowing you on. I can feel the horn section going through my back and out through the front. It's a wonderful noise and not many people get that privilege. It's exciting, walking into that dark amphitheatre and hearing that music. You'd have to be made of bloody stone not to be affected by that."

Preparations for this latest edition of Britain's most famous talk show began 30 minutes after midnight, some 18 hours before the start of recording, as staff at the London Television Centre, on the south bank of the Thames, began setting up the lighting rig inside ITV's largest studio.

By the time Holloway's sound check finishes at 3.45pm, Parkinson is with his research team viewing the video clips that will be introduced into his interviews. Ahead of his dress rehearsal, a dark jacket and a selection of ties have been laid out for him. With the exception of one navy-coloured club tie, they are in bright hues - an orange one by Hugo Boss, a red patterned creation by Dolce & Gabbana, a lilac design from Harrods.

But Parkinson's primary concern at this point is that the leather chairs on his semicircular stage are correctly positioned. It is an issue over which he is "pernickety to the point of being obsessive," he says. "I've done so many talk shows where you are sitting down with your knees on your bloody chin and you can't see anything, or the guests have to lean forward to see the host, or there's a desk between them, which is never a good idea. A lot of thought has gone into the kinds of chair we have and the positioning of those chairs."

Parkinson is an obsessive not just over the placement of furniture but his preparation for the show in general. He began work for this production on Monday morning, brushing up on his guests by reading Wilder's new novella My French Whore and viewing Hislop's BBC4 documentary on Robert Baden-Powell, Scouting for Boys. "I've learnt over the years how to assimilate research," says Parky. "You can't just laboriously read a book, you've got to be able to cope with reading two or three books in a week for research purposes, never mind a pile of documents."

When Parkinson was lured to ITV from the BBC in 2004, the coup for Britain's largest commercial broadcaster was tempered by snide comments that the traditional talk-show format was past its sell-by date and that the king had been usurped by the corporation's new champion, Jonathan Ross. On the 11th storey of the building, commonly known as "The Parkinson Floor", both suggestions are flatly rejected.

In his office overlooking the Oxo building, Mark Wells, the executive producer of Parkinson, says: "We wanted to make it the gold standard of TV talk shows and were prepared to do whatever was required to maintain that position." For example, the black leather chairs on the set were selected only after hours of discussion. "They had to be made of the best-quality Italian leather, very contemporary but with a nod to the past and the heritage of the show. Michael's last set at the BBC looked like someone had been to the office- supplies shop."

Parkinson is all about "getting the biggest stars you can get", so there is a degree of pampering and each guest is given a "Parkinson"-inscribed Montblanc pen. Unlike his rival Ross, Parky does not try to introduce his audience to new talent, except in the musical part of the show, where he has given career-changing exposure to acts such as Razorlight. The talking guests should need no introduction.

The Parkinson show's researchers and assistant producers have to be sufficiently experienced to be able to conduct preliminary interviews with major stars, ahead of providing briefing notes for Parkinson himself. But even at 73, the presenter remains fresh and relevant, Wells says. "He has a journalist's instinct, he's also a fan, in part, and he's genuinely interested in people. That combination makes him an extraordinary host."

Down on the ground floor, the guests arrive and the host does his best to put them at their ease. Stewart and Hislop have both done the show before, but Wilder is more of an unknown quantity. Parkinson has watched him appearing, somewhat uneasily, on the US show Inside the Actors Studio. "I could see from that show he was nervous, and doesn't like doing talk shows. He's jittery, so I had to reassure him that this wasn't like the [David] Letterman show, all about jokes and standing on your head being funny. On my show, you can actually do an interview and talk. But I never say, 'Look, this is what I'm going to ask you about'. You can't rehearse an interview. If you do, the guest will turn to you, on air, and say, 'As I was telling you in the dressing room...'!"

In make-up, where Chrissie Baker is applying the slap, Parky makes a minor faux pas in failing to recognise Stewart, known to the world as the actor behind Star Trek's Captain Jean-Luc Picard of the USS Enterprise. "I saw Gene Wilder and there was a big well-made guy with a bald head and white T-shirt standing beside him. I thought, 'That's his bodyguard'. So I started talking to Wilder and then realised that the bodyguard was Patrick Stewart! He did look different in this gym outfit. He's incredibly well toned, really fit. Looks like my old Army PT instructor."

At 5pm, the host retires to Dressing Room 1 with a cheese sandwich from the ITV canteen. Further down the corridor, his son, Mike Parkinson Jr, who produces the show with Steven Lappin, are making final preparations. Mike, who was an experienced producer at the BBC but didn't work on Parkinson, began working for his father for the first time when Michael Sr persuaded him to join him at ITV. "Being his son, I suppose I have grown up with the show. I used to be in the studio as a child and watch recordings. What has taken me by surprise at ITV has been the reaction of the audience. When he walks down the stairs, it's quite extraordinary."

In the studio, the floor manager Quentin Mann is getting the audience to Mexican wave in anticipation of the appearance of Parky. The warm-up comedian Ray Turner goes through a routine of dubious comedy, encouraging two men from the audience to put black stockings on their heads and sing along to The Drifters' "Under the Boardwalk".

At 6.30pm, the wait is over and Holloway's orchestra comes alive: "Dat-diddly-da-da-da!" Parkinson skips down the stairs, nods to the audience, nods again. He has ignored the production team's selection of bright ties, and chosen the serious navy one. He introduces Stewart as "the furniture salesman from Yorkshire who became a global superstar".

Seconds before each show, Parkinson stands on the blue landing at the top of the stairs and contemplates whether he is properly prepared. "In the end, it's about being settled yourself. It's about being at the top of the stairs and feeling, 'If I go on there now, knowing what I know, having prepared as I have prepared, sober and in my best suit, then if it goes wrong, it might not be my fault'."

Tonight, he seems confident that he is on solid ground. "Patrick Stewart is a natural, he just chats away," he says later. Experience has taught him that if an interview is not working early on, then it's not easy to turn it around. "You don't have that much time. You can allow yourself two minutes to get them settled in, but if, after that, they're not settled, then you're buggered, quite frankly."

The Stewart interview closes, allowing Parkinson (the boy from Barnsley who became the champion of chat) to introduce another Yorkshireman: "A gas-fitter from Sheffield who became a music legend... Mr Joe Cocker."

The jobs of Lappin and Michael Jr are made a little more difficult by the fact that Parky does not wear an earpiece. Instead, Mann stands at the front of the stage holding up pieces of A2-sized card with prompts written in 6in-high letters and chosen by the host himself. "When I go on, I give Quentin about eight listings as an aide- memoire - I never look at my notes unless there's a break in the proceedings. That idiot board is there to actually remind me. I had 'Mother', which indicated to me, in the case of Gene Wilder, that he had had a bad time with his mother. And 'Father' for Patrick Stewart."

Ian Hislop is the next guest, and Parkinson is an admirer of the Private Eye editor. "He's very good to camera, he has a wonderful enthusiasm, and he doesn't mind taking the piss out of himself. And I think he's a very good journalist."

After Cocker has belted out his hit, "Unchain My Heart", Wilder is at the top of the stairs. This is the interview everyone seems less confident about. "No matter who you are, when you walk down those stairs and there's all that bloody music going, and the audience there, it's not easy to keep your nerve and collect your thoughts. Even actors find it difficult to just play themselves," reflects Parkinson. "A lot of them - like Wilder - find it difficult because they think the expectation of them is that they will come on and pull a rabbit out of their trousers and start being funny, or come on in a clown's outfit. Even if they don't see themselves like that."

But the star of comedy classics such as Blazing Saddles and The Producers rises to the challenge and engages in a discussion of great breadth, encapsulating both the humour of his working relationship with Mel Brooks, and the pathos of his battle with non-Hodgkin's lymphoma.

The show ends with a series of recordings of the audience applauding over the end to the theme tune - "Dat-diddly-da-da-da!" Harry Stoneham wrote the tune in the BBC basement more than three decades ago, and the host doesn't seem fed up with it, demonstratively banging out the rhythm on the arm of his chair.

The guests go off to have their picture taken and to sign a book that Parkinson will later donate for a charity auction. In the Green Room, there are bottles of Heidsieck champagne laid on, and posh chocolate biscuits from the show's sponsor, Bahlsen.

An hour-long show has been recorded in just 80 minutes. In the edit suite on Friday, 74 minutes of footage must be trimmed to 50 minutes, compared with the 70-minute show that Parkinson had on the BBC. "Fifteen minutes over is acceptable, anything more is not," says Parky. "Fifty minutes is the ideal time for a talk show, and ITV has taught me that. It had got flabby at the BBC.

"When I first went to ITV, I thought, 'Bloody hell, is this the end of the talk show as I know it?'. But I've enjoyed working to the new discipline. It's now a better show."