If there is a church door open, I walk in and pray. I very seldom ask for anything. I thank Him

Sir Jackie shows me the ring first. There are two words on it, spelled out in gold: integrity and care. The former racing driver says the words mean that if he says he'll do something, he will definitely do it, which is probably why his schedule is so intense. Today, for example, there are business meetings, charity events, speeches and dinners. Yesterday, he was in Oxford; today he is in Edinburgh; tonight he will be in Barcelona.

I ask him why, at the age of 73, he lives like this, why everything is done at full throttle, and he says the speed of his schedule is probably because of who he is inside: the speed in him.

Then I spot the second little detail: the Rolex watch. Sir Jackie has been an ambassador for the company for years but it's just one of the big-name companies he does business with. "Without sport it might not have happened," he says. "I might have been in the dustbin, but I was in a sport that was commercial." He's made a lot more money in business than he ever did in motor racing, he says – and he made millions in motor racing.

Now for the third detail: the pound coin in his pocket. Before our interview, I met Sir Jackie at a charity event in Glasgow and he tells me he had simply spotted a pound coin on the floor and picked it up. Is this the canny multi-millionaire looking after the pounds and pennies? Not really.

"If it had been a piece of paper, I would have picked it up," he says, "because it was a clean carpet. I saw that it was money – if it had been a penny, I would have picked it up. It was there and it shouldn't have been."

Which proves another quality of Sir Jackie's – one he certainly showed in his racing days in the 1960s and 1970s. It showed in the way he could see every little detail of a course even at 165mph. He is a perfectionist, a details man, a man who likes everything to be just-so. He's good at cleaning floors and windows, for instance. "I would make a very good window cleaner," he says.

Taken together, it's all of these little details that reveal who Sir Jackie Stewart is: a Scotsman proud of his achievements, a businessman who loves the success it has brought him and a hard worker who is probably a little afraid of what might happen if he ever slowed down. He also can't bear to be out of the loop – he has three phones with him at all times: one for incoming, one for outgoing, and one for family.

So much for the small details, but what about the big questions, and the biggest of all: mortality? We get round to the subject after talking about Sir Jackie's old dog, Boss. When he lost Boss, he felt like part of his soul went with him, but he says he has no fear of death himself. I ask him if that lack of fear comes from faith.

"I don't go to church," he says, "but I go into a lot of churches. If I'm walking in any country I'm in and there's a church door open – I don't know whether it's a synagogue or a mosque or Church of England or Roman Catholic – I walk in and pray. But I very seldom ask for anything now. I thank Him. Every single day something happens to me, I think: 'How did that happen? Thank you.'"

Such humility might sound cringeworthy coming from some famous people but not with Sir Jackie. Read his memoirs, Winning Is Not Enough, and the quality that comes through more than any other is modesty. Part of this comes from the difficult educational start he had. "Probably the greatest disappointment in my life is my education," he says. "If I'd had education, I would have done much better. I live in Switzerland but I can't speak French and that's because of the difficulty I had at school."

The difficulty was dyslexia, which Sir Jackie has made one of the big campaigning issues of his life. I'm meeting Sir Jackie just before he addresses an event in Edinburgh called Informatics Ventures Engage Invest Exploit. It's a showcase for investors of promising new technology projects, but Sir Jackie confesses he doesn't have an iPad or an iPhone. In fact, he doesn't even use the internet and that's because he can't find the words on a keyboard because of his dyslexia. He can make a phone call but can't send a text. His emails are dictated and then typed up and sent by his PA.

Sir Jackie is not complaining about any of this – far from it, he just gets on with it. He doesn't get stressed or anxious or over-emotional. He says that in his motor racing days, the key to success was learning to control his emotions as efficiently as he controlled the car. "Control your emotions and you will deliver more," he says. "In motor racing, if I got angry, the penalties were high. It was no good trying to get back at someone, you had to get round them. So at the start of the race, I had literally no emotions."

Sir Jackie takes pretty much the same approach to his body and his health. Last year, he fainted while flying from Geneva to London but instead of getting upset, he got analytical. "I'd had muscle pain in my back from sleeping the night before and when I sat in the plane it got worse because of the altitude. Because of the muscle pain I wasn't getting enough oxygen, so I fainted."

What Sir Jackie did next was head straight for the Mayo Clinic in Minnesota for a comprehensive check-up. He goes there every year for a two-day health check, a kind of human pit-stop. I tell him it sounds like he takes the same approach to his body as he does to his cars.

"Same thing," he says. "I'm not as young as I used to be. I've got a metatarsal in my foot right now that used to have a cushion – flesh and blood – but that cushion over the years has deteriorated and is not as thick as it used to be. Now I get a sore foot and that's wear and tear in the same way as a tyre or an exhaust system. Why wouldn't I look after my body as diligently as I look after my cars?"

He starts talking a little about those cars: how it takes five years to build a Formula One car, how he still occasionally drives on a race track "as fast as it needs to be" and how he still loves driving. We also talk about the cars the three-times F1 world champion drove in his heyday and how they were always painted Caledonian blue to show off his Scottishness. As he's already said, he lives in Switzerland but he also has a home in Buckinghamshire, so how is the Scottish/British balance these days?

"I'm a Scot through and through," he says. "I'm a reasonably canny Scot – I think I've been careful with what I've done in my life. I survived. I never drew blood from my body driving a racing car."

I ask him if he's formed a view on independence yet. "I have a high respect for Alex Salmond – I think he might be the best politician in Britain today. The independence thing is a different question because I'm not living here and I therefore can't understand it to its fullest extent. And I don't vote. As a young sportsperson, you start making quite a bit of money, you get approaches from all the political parties for support, so I made a decision I would never make a contribution to a political party and, if I didn't do that, I shouldn't vote."

Basically, Sir Jackie thinks sport and politics shouldn't mix – it's why he supported the Grand Prix going to Bahrain and still does – although he doesn't have the same qualms about mixing sport and business. Quite the opposite. He has direct lines into the headquarters of some of the biggest corporations in the world and he works by personal association and friendship, including most controversially Fred Goodwin of RBS ("it wasn't one man who caused the economic collapse; why would I turn my back on a friend?").

These days, in fact, Sir Jackie sees himself more as a businessman than a sportsman although it all comes back to F1. Sir Jackie is proud of the sport, his achievements in it and the decisions he made. Just a few hours after our interview, he will be flying to Barcelona for the Grand Prix and, from there, on to another string of appointments, his three phones by his side; hard-working, busy, at full speed but calm.

Sir Jackie Stewart Former racing driver

Career high: Winning my last F1 World Championship in 1973.

Career low: The death of my friend Jim Clark [killed in a motor racing accident in 1968].

Best trait: Attention to detail.

Worst trait: Having dyslexia.

Biggest influence: The Argentinian racing driver Juan Manuel Fangio.

Favourite meal: Eating at home with my wife, Helen.

Favourite holiday destination: Western Highlands of Scotland.

Favourite film: Dr No, pictured.

Favourite music: The Beatles.

Last book read: Dick Francis.