Putney, southwest London, one evening last week: Marco Pierre White was with friends having dinner inside his restaurant, Frankie's; outside his driver waited in the Range Rover. Three youths strolled past the car, glancing in through the window. A few steps farther on, they turned and swaggered back to the car. “When they got to the windscreen they stared at me. I did not know what to think,” recalls the Japanese man who was behind the wheel.

“Then one of them said, ‘Hey, are you Mr Ishii?' I said, ‘Yes.' They said, ‘Can we have our photograph taken with you?'” When the posing was done, the youths went on their way without requesting so much as a scribbled autograph from Ishii's famous employer.

Takanori Ishii, 57, has became famous through Marco's Great British Feast. The ITV1 series has shown White travelling the nation to unearth the finest produce that he will serve to 220 guests in tonight's final episode. Ishii has been the loyal sidekick, smartly dressed in a three-piece suit and driving White from region to region.

Viewers have seen Ishii as White's stooge (there was the moment when White asked him to stand beside a cow to see who was taller - the cow won by a few inches). They have seen Ishii as White's taster (“Mr Ishii, try this squirrel pie”). We know of White's life: his mother died when he was aged 6 and he was raised by his father on a Leeds council estate; he grafted for kitchen masters such as Albert Roux and Raymond Blanc; at the Hyde Park Hotel he became the first British chef - and the youngest - to win three Michelin stars.

But who is Ishii? Why has he stayed for 14 years with White, a notoriously demanding perfectionist? And why, for heaven's sake, is he known as Mr Ishii rather than Takanori? According to White, Ishii is more than a chauffeur. “Mr Ishii is a friend, a PA, a confidant,” White told me over drinks one night. He added: “Mr Ishii is like the Pope. He sees everything and hears everything but says nothing.” In real life Ishii is as you see him on screen - quiet and quietly spoken, a gentle gentleman. Compare his mild nature to White's extrovert character and it becomes clear why White says: “He is the yin to my yang.”

Ishii was born on the Tsushima Islands in southern Japan and grew up, an only child, with his father, a town councillor, and mother, who worked in a butcher's shop. “I was always eager to learn about cultures outside of Japan,” Ishii says. He left Japan in the Seventies and came to London to study English.

He worked in Burberry as a salesman, selling expensive clothes to West End shoppers, and was an interpreter. “Then I met a Japanese man who wanted to invest in a restaurant in London,” he says. “He bought Mirabelle and that is how I came to work there.”

Ishii became a director and restaurant manager of the Mayfair restaurant. In the mid-Nineties, White was scouting for a new restaurant and wandered into Mirabelle. “I shook his hand and we chatted for three hours. At that point Mirabelle was not for sale, but for months afterwards he kept in touch by phone and he'd come into the restaurant some nights and stay for five or six hours. I was very impressed by him. He talked about ‘the mechanics' of the place and wanted to see how it could be run if he owned it.

“He also told me that if he bought Mirabelle he would continue to employ the staff. This was very important because in Japanese culture it is wrong to lay off employees. There were others who wanted to buy Mirabelle but the deal was about more than just money. Marco was the right person to keep the restaurant - an institution in London - alive.”

Zoom forward a year. White had secured Mirabelle and retained its staff. He had also established a close bond with Ishii. “Shortly after Marco took over we started to concentrate on French cuisine,” Ishii says. “It is an important part of my culture that once I have assessed my employer as a good man I have to work hard and repay my boss's loyalty. I'd say to him, ‘Marco, please tell me if there is anything I can do for you.' He does not drive so I started to pick him up in the mornings and bring him into work. As the relationship developed I had to make a judgement. I had to assess whether or not Marco was a worthy person for me to devote my life to. I could see that he is a strong person and that he is not ordinary. He is not greedy or arrogant, like many people. He is now like a brother I respect. Many times I have asked him to call me Takanori, but he does not comment. He calls me Mr Ishii because he wants to show me respect, and all of his friends know me as Mr Ishii.”

Politeness slips from time to time in this friendship. “Sometimes he will bark at me. But I am a Buddhist and I pray every morning and every night. This enables me to find wisdom, strength and life force.” Ishii is the calm to White's storm.

“If he has b******ed me, I'll try to work out why he has been like that. He might explode because of the pressures. I will say, ‘I am so sorry, Marco. It is my mistake.' Then he will say, ‘I am the one who is sorry, Mr Ishii. It was my mistake.' I like him. He is honest and straightforward, and he has a mischievous sense of humour. One night I stayed at his place in the country and the next morning I had to catch a train. I was in a rush and looked around for my shoes but couldn't find them anywhere. Marco had put them on the hat stand but they were so high up I couldn't see them,” says Ishii, who is 5ft 6in (1.7m).

White does not do sleep (much); his days are long and inevitably Ishii is required to be on call. The assistant is always well-mannered, polite and charming and White says he has never seen Ishii lose his temper. So what are his secrets for staying serenely chilled?

“I need to look after my health, otherwise I will have difficulties in meeting Marco's requirements. I take vitamins, try to have a good sleep and eat Japanese food. I take finely sliced cucumber, which is marinated for a moment in salt before it is washed. Then vinegar and sugar are added to it. Stress shows itself in the stomach and this is particularly good for dealing with stress.”

There are perks of the job. He and his family - his wife, Yoko, a hairdresser at Vidal Sassoon, and daughters Emiko, 22, and Takae, 21 - receive invitations to dine at White's restaurants. Ishii has also been made a shareholder of the Knightsbridge branch of Frankie's. The family lives in Ealing, West London. “I like to watch movies. I like very much Julia Roberts and Russell Crowe. Family is very important to me. That is what brings me happiness, along with meeting people. My family appreciates there are times when I have to leave home very early in the morning and will not return home until late at night.”

TV will not change him, he says. “I am not interested in being famous. I am more concerned with getting on with my life. I want to carry on working with Marco, if he wants me to continue working with him. Life with Marco can be hard but also very funny. If he thinks I'm driving badly, he'll say, ‘How close did you come to killing that pedestrian, Mr Ishii?' And I'll say, ‘About 6in, Marco.' We have lots of jokes.”

Marco's Great British Feast, tonight, ITV1, 9pm

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