One last morning with Chris

It's five to six in the morning and as we speed down The Mall in his chauffeur-driven car, Chris Tarrant sticks his head out of the window like a bouncy golden retriever and howls, his blond hair ruffling in the wind.

"Good morning Vietnam!" he shouts, before letting out a few more "wooooooooo"s loud enough to wake the Queen. He has done this every morning since he started his Capital radio breakfast show in 1987. His head safely back in the car, he looks much more awake than when I met him, coffee in hand, outside his gated mansion in Surrey at 5am.

Then, stumbling in the darkness to the car where his faithful driver, Jim, waits for him every morning, he looked as if he was sleepwalking. He'd only had three hours' sleep, having filmed a celebrity special of Who Wants to be a Millionaire? the previous night ("Jon Snow was on," he says, "he said he always listens to Capital in the morning, not the Today programme").

Tarrant is charmingly shambolic in the flesh, certainly not the sharpsuited, suave presenter we're so used to seeing on the telly. He is wearing shapeless black trousers with a few stains, a blue polo shirt and a black leather jacket with an elasticated waist that he's surely had since the Eighties. He looks absolutely knackered, far older than his 56 years.

This is one of the reasons he is giving up the breakfast show after 17 years. "I don't want to get up at 4.30am any more. I'm tired and I want to see my kids, not just kiss them on their heads before I leave the house," he says.

"I do feel as if I've missed out on a lot of my youngest two growing up, a lot of the normality. I've been doing the show longer than they've been alive so they don't know what it's like to have me around in the mornings. I'm actually looking forward to doing the school run. But I do want to go out on a high."

During his time at Capital, Tarrant has made it London's most popular breakfast show. He's not quite in the Smashy & Nicey league yet (though that leather jacket is worryingly close) but, given a few more years at the station, it's easy to see how it could go that way. His jokes are the ones your dad would chuckle at and he looks far more at home playing the Rolling Stones's Brown Sugar, drumming away on the desk, than Blazin' Squad ("Who is this?" he asks his producer when the track is playing).

It's a tense morning in the small studio overlooking Leicester Square - the computer, with all the show's jingles on it, has gone down and there are engineers scurrying around; the sound in the studio isn't working properly and, as the producer worryingly puts it: "It feels like the whole thing is going to crash."

Tarrant puts on his best geeky voice and teases the engineers about "transponders"; his ability to defuse the situation makes a huge difference. You wouldn't even know the technical problems were getting to him apart from the fact he keeps saying "bum" over and over, the schoolboy naughtiness occasionally giving way to the odd "f***". It's all off-air, of course; he says he's never sworn on air, not counting the time when he called his station "Crapital FM" by accident.

He had flicked through the papers in the car on the way in, his driver stopping at the same garage every morning to pick them up along with more coffee. The Nepalese garage workers are very upset they won't be seeing Tarrant at precisely 5.20am from now on. "Tell Mr T we're going to miss him," they tell his driver.

Whenever Tarrant sees a story he likes and can talk about on the show, he rips the page out, screws it into a ball and stuffs it in the inside pocket of his jacket (I assume he'll bring them out in the studio to refer to but they never materialise again and I wonder how many weeks' worth of scrunched-up stories he still has). He doesn't need them anyway.

His producer, Sarah-Jane, who is glamorous and in full make-up when most people are still in bed, has already been at work for some time and has been through the papers for him. Neither of them thinks there's much in them today worth talking about; after all, the war on terror isn't exactly Capital breakfast show material.

On air, munching his way through a bacon sandwich (he thinks nothing of talking with his mouth full), Tarrant steers the show through the usual mix of pop music, chatter, and the ritual but harmless humiliation of the general public. One man who phones in to repeat a tongue-twister three times is told he's "pathetic" but, coming from Tarrant, affable as ever, he can't feel offended. Tarrant holds the show together, even when features don't work.

Caroline, a mortgage adviser, calls from the 119 bus on her way to work in Croydon for "Flirty at 8.30", where Tarrant matchmakes listeners. He tells me it's Jon Snow's favourite part of the show. There's a tense moment when the boy she has named on air for Tarrant to call won't answer his phone, but he laughs it off, offering to fix her up with a caller who has offered to take her on a date instead. "Even though he sounds like a psychopath, Caroline? You're not fussy, are you?"

Tarrant is the breakfast show. Becky Jago, a young, pretty blonde, reads the news and weather and occasionally chips in when she can get a word in, which isn't often. Given the chance, he could talk for hours. "It's not remotely difficult but don't tell anybody that," he says. "I can't believe I get paid for doing this."

It certainly doesn't look difficult but that has to be because Tarrant is such an old hand. He is quick, but not a natural comedian. There is a news item about the danger of Viagra damaging male fertility and Tarrant butts in with a "tell me about it", which wears thin after he does it during several news bulletins.

When a child called Elliot rings the show, Tarrant does a rather predictable "Elllliiottt" impression from ET several times, even though it means nothing to the eight-year-old.

It's not the most dangerous radio around - even his own team start yawning when he keeps one caller talking about fishing for several minutes - but it's precisely this comfortable, familiar tone that keeps his 1.2 million fans tuning in every day.

It's April Fool's Day, and when he plays Justin Timberlake's Cry Me a River, he also plays a pre-recorded skit of the team talking, appearing to be live on air, having forgotten to switch the microphones off.

"I don't know what people see in Justin. He's a bit weedy," he says, before launching into a tirade about how annoying his wife is and how he can't wait to leave his job. The phones start going and the texts come in: "CT, we can hear everything you're saying," says one concerned listener. "Turn the mics off !" writes another. The whole studio is falling about.

Tarrant decided last year that he would leave. It's not as if he needs the money - even without the £1.3 million he gets from Capital he is set to earn upwards of £7 million this year from Millionaire, Tarrant on TV and a couple of new programmes. He also charges upwards of £8,000 for personal appearances and, as well as the house in Surrey, he has homes in Stratford-upon-Avon and the South of France.

So was it the money that made him get up at 4.30am every weekday for 17 years? "I think it was at first," he says. "But I just really enjoy my work, I get such a buzz from it. All I've done is share with other people what

amuses me." He has made a career out of being the bloke-next-door, no matter that most people don't live in a leafy street full of millionaires in Surrey.

It seems as if Tarrant has been on television for ever ("Longer than you've been alive," he points out. "God, that makes me feel old"). His first big break was the anarchic 'Tiswas, the Saturday-morning children's TV show he fronted from 1974 to 1982. The show's success meant the former teacher from Reading was suddenly a big star, but it also cost him his first marriage.

He met his second wife, Ingrid, now 49, in 1985 when they both

worked for TV-am (he was reading the news, she was a reporter). Their relationship is one of the most stable in showbusiness but, of course, there have been ups and downs.

"I think it has been quite hard on Ingrid, because I work so much, but we always make time for each other. We're a close brood," he says of his two children with Ingrid, Toby, 11, and Sammy, 15, and the two each from their previous marriages. "I'm looking forward to spending much more time with them."

But his family's gain is his listeners' loss. They are distraught to see him go, if the hundreds of texts and emails he has received are anything to go by.

One woman, knowing his favourite pastime, has sent him some fishing equipment ("It's good kit as well," says Tarrant, "she knows her stuff ").

HIS listeners have been with him through the Thatcher era, two Gulf wars, the death of Princess Diana ("That was the week when I really realised what radio meant to people," he says. "It became a way for people to show their grief "). It feels like the end of an era but Tarrant is realistic. "It will go on without me," he says. He is generous about his successor, Johnny Vaughan, another television-presenter who trades on his blokeish charm. "If he can harness all the energy he had on The Big Breakfast, he'll be great."

So, after today's show, with 17 years of pre-dawn starts behind him, he will hang up his headphones. He says he won't cry and that he can't wait to go (he's only half-joking). Then he'll jump in a car and speed off to catch a plane to Barbados with his family, where he says he will sleep a lot and watch the cricket. I hope he howled a last goodbye to his London listeners out of his car window on the way. You can't imagine Tarrant going quietly.