I knew that Jamie Oliver was successful, of course. How could I not? I knew that he made television programmes and led social crusades and sold cookbooks by the container-load, that there was his website and his apps, that he'd won an Emmy in America, that the mortar and pestle my mum gave me for Christmas has his name on it, and that a rash of Jamie's Italians have sprung up on high streets up and down the land.

And yet, it turns out, I know hardly anything. I don't know about his holding company, and the scale of the retail operation, and that his restaurant business has outlets opening in Brazil and India and China and Russia and who knows where else. I don't know that Jamie's Italian turns over £100m a year, the holding company another £35m a year. I've never even heard of Barbecoa, his barbecue chain, Recipease, his cooking school, Union Jacks, his fish and chips venture, Jamie's Italian Trattorias, a restaurant sub-brand not to be confused with Jamie's Italians. Since we first saw him scooting around London in The Naked Chef, he's become an entrepreneur worth an estimated £225m who employs 8,000 people. 8,000! And he's in charge of it all. While still doing all the cheeky chappie stuff and still making cooking programmes and berating Michael Gove and banging on about people with big-screen TVs eating cheesy chips.

When I turn up at his offices near Old Street – so-called Silicon Roundabout, the hub of Britain's startup scene – to interview some of the people involved with the tech side of the business, we can't, initially, find anywhere to sit. There are five floors in all in the 50s block but they're all full. "You need a bigger office," I joke, not realising until later that it's just one office building out of a whole cluster. There are multiple buildings filled with multiple young folk all dedicated to burnishing the Jamie Oliver brand, including a whole team devoted to his social media, his apps, his YouTube channels. Because while it's not quite correct to say that technology is at the heart of all Oliver's businesses, it's certainly at the cutting edge of his media empire (as separate from his retail empire and his restaurant empire) and drives everything else. In just over a year, FoodTube has acquired nearly a million subscribers and is now the third biggest food channel on YouTube; DrinksTube has just launched; the app was, within a few months of launch, the most lucrative on UK iTunes; the website has eight million visitors a month and has just walked away with three Webbys, the Oscars of the online world.

Jamie Oliver no longer is a TV chef, or a campaigner, or a cookbook author, or the owner of several chains of restaurants, or at least he is, but he's also, as he tells me later, "a very strange brand, a celebrity disruptive force". Though moments later, he says: "It's a really weird thing to try to convey without sounding like a nob."

But it's true. He is a strange one-man celebrity disruptive force. One who, somehow, manages to get away with it without sounding like a nob. It would be impossible to explain Jamie Oliver to a visitor who'd just dropped by from Mars. Because alongside all the noisy stuff he does, he is also quietly and strategically using all the weapons at his disposal, many of which are technology based, to actually try to make a real difference to global public health. And yet, he is also still Jamie, recognisably still the fresh-faced, mop-topped Essex boy with a lisp and a habit of babbling words that don't quite make actual sentences; whose company makes nearly £10m profit a year and yet who's clearly not all about the money. When I cross the road, to another office, another five storeys of Jamie-dom, to a light and airy room hung with modern art and meet the man himself, I don't mean to ask him about tech right from the off but the first thing I notice is that he's wearing a Jawbone wristband: the activity tracker that tracks and quantifies how much you sleep and exercise.

"I'm testing them all. There's a bit of an arms race going on at the moment between different manufacturers."

Why are you testing them? "I'm just quite fascinated by it all. There's lots of different bits of technology that measure energy and altitude and movement and weight and temperature and heartbeat. There's a lot of data that can help different types of people in different ways every single day. That's brilliant. I love it. And I'm testing them all: Fitbit, Jawbone, Nike Fuel Band, Withings. It's the energy-in that's the sticking point at the moment."

You mean quantifying how many calories you're actually eating? They don't seem to have cracked that, do they? "Well, they will. It's just going to be how to handle huge amounts of data. But there's technology called TellSpec that can tell exactly what is in food or blood or piss. It can tell if there's metals or hydrogenated fats or what kind of vegetable and it's very interesting technology that can be used in phones or with phones in the not-too-distant future." His "dream", he says, is that "stuff like these wristbands could really help to resist the rise in diet-related disease and truly make a difference in a sustainable way".

"I believe that 100%. Every six months we have a seminar here at the office and we invite world-leading, interesting, fascinating dudes: GPs, specialists, campaigners etc. We get them at a table and these are all wonderful people who are fairly siloed. And everyone's quite bitter about it."

Why bitter? "Because they say, 'I did this but then someone else came along and then they left'. Because the government comes and goes every four years and, for the love of God, it's just such a waste of money. Change needs to happen everywhere. To save money and to save lives. And if I'm boring you, slap me and move on, but to know how people are living and what their patterns are to have a more holistic approach that a GP could have access to could be huge."

But then, it's perhaps no surprise that he's so evangelical about technology. It taps into the same place that seems to have captured his enthusiasm for food. He is, he says, a "self-confessed geek". What do you mean by that? "I just love intense, high-level weird stuff." Like what? "Anything. You want to talk about biodynamics? You want to talk about making beautiful fly hooks? You want to talk about the best wild salmon cure? The best salt on the planet?"

And yet, this was the boy who left school with two GCSEs. Who's struggled all his life with dyslexia. Do you think your school career might have been different if certain technology that's around today had been around then? "My nephew is dyslexic too and, unlike me, they get fully checked, they get special assistance in class. He's a really bright boy but he still struggles with technical bits. So … he can, I've forgotten the word? Touch type? He can touch type. If you're dyslexic you struggle with writing, but if you can touch type it's like you're not dyslexic so technology has the capacity to be a wonderful thing."

I've interviewed Oliver before, at TED in California, the year after he'd won the TED prize and was feted by west coast tech gurus, billionaires and campaigners who hoped his self-styled "food revolution" might make a dent on the nation's eating habits. It was the first time a celebrity, a TV star, had won the prize, but in some ways, TED and California was the natural home for his combination of can-do zeal and hard-to-repress optimism. Though, in the end, as anyone who watched his US reality show saw, it did manage to repress it; the scale of the problem in the US, the dysfunctionality of its food industry and food-related health problems was so vast and intractable that even Oliver's cheery Essex boy charm couldn't make much headway, particularly after the TV show was canned.

He still has a base in California. And one upshot is that as a result of the time he's spent over there, he's been exposed to various Silicon Valley types. He scoffs when I ask him about the British equivalent, Silicon Roundabout, AKA Tech City, even though his headquarters is slap bang in the middle of it. There's some "interesting boys" doing interesting stuff, he says. "But you just can't put it in the same sentence as Silicon Valley! It would be like my village versus America in a war. It's ridiculous."

He met "the Jawbone boys" a couple of years ago. "They're friends with the Instagram guys, Kevin and Mike. I met them through a friend I used to cook with who now has a restaurant in San Francisco. That's the thing about San Francisco, it's quite hard not to have a coffee and meet someone who's doing a startup. So I met Kevin and Mike and they'd just started an app called Aperture. I'm a geek and it was just a good bit of tech: if you took a picture you could add depth of field to it. And then they built in a camera and filters and, of course, that's Instagram."

So, you met them before they'd done all that? "They'd been going a handful of months and so I was one of their very early adopters but only because I enjoyed it and because it worked."

He's been hooked ever since. "I use Twitter, but the challenge of getting so much out into so little digits, and it's just words … I'm no psychologist but it just seems to bring out the worst in humans. It can provoke bile and I try and avoid negativity as much as possible. With Instagram, because it's just images, it's a much warmer audience."

Words have always been Oliver's sticking point – despite the fact that he describes himself as dyslexic in his Instagram profile, he says the "only thing that pisses me off" about it is that he's always being picked up on for his spelling. But it's no surprise, really, that he is such a natural at social media, because he's such a natural, socially. Zoe Collins, who's head of Fresh One, his TV production company, met him at Radio 1 during the first series of The Naked Chef. "She was a radio producer and I grew up on a farm so we just became buddies and I told her one night, 'Look, you go work in TV and get some TV stripes. I'm going to work out how I can make enough money to create a business and then I'll build a TV business and you will come and work for me.' And that's how it happened." But there's lots of people here who've had a similar experience. He meets somebody, believes in them, and then he goes: "Come into my world and then we'll work it out."

There's no doubt that he's loyal. And that his business has been built on relationships. On his way to the photoshoot, I see him give a white-haired secretary a hug and she later tells me she's worked with him from the very beginning: she was his accountant's secretary and she came along with the package when he made him his first managing director. He still owns 80% of the company and friends and family own most of the rest. It's a highly commercial operation – to give just one example, the most watched video on his YouTube channel is actually an ad for EE featuring Oliver and Kevin Bacon, online advertising being his latest venture with its latest spin-off company, Fat Lemon – but it also has Jamie-ness running through everything it does. His Instagram is his authentic voice and the company, the crusades, the mission to improve the public's health through what they eat, is still at the heart of it all. Somehow, he has pulled off that rare trick of making money by not selling out but by remaining true to his core values.

FoodTube, the online video venture, which is the recipient of the latest big marketing push, and the reason why this interview is taking place, is a prime example of both these impulses. It's an obviously commercial space to be pushing into. Collins tells me that "it was quite a revelation to us how big the YouTube food celebrities were but then I think it was a surprise to the rest of the TV industry too". It has made cookery stars out of complete unknowns: a self-taught American Italian home chef called Laura Vitales has 1.3 million subscribers; SortedFood, a bunch of young British men who seemingly came from nowhere have 800,000; both Vice and Buzzfeed have recently launched their own food channels.

FoodTube's USP is that it isn't just Oliver's channel, it's also a platform to launch new chefs. Kerryann Dunlop, one of the original team at Fifteen, the social enterprise Oliver built to help train unemployed young people, has her own channel on the site, on the back of which she's just published a book of her recipes. It's perfect Oliver synchronicity: it gives a Fifteen graduate a boost, it provides content which is what every YouTube channel needs, and it brings in advertising and sponsorship deals – Bacardi, for example, is already on board.

Presumably part of the reason you've had to go out and find new talent is because there's not enough of you to go around? He shrugs. "The minute you start getting published in 120 countries and broadcast in 160 countries and doing the Food Revolution Day in 90 countries … I can't physically be in all those places. So, you start to think: 'All right, I'm 38, British boy, I think my heart is in the right place, but what am I to do? All these clever strategists and CEOs think I have a master plan and I haven't really. All I know is that I want to get really good content out there, more standardised content that I think will make a dramatic, sustainable, exponential difference to people's cooking and shopping habits.

"And these tutorials and how-tos are really, really popular. People want to know how to skin a rabbit. They want to know how to make a pie. They want to know how to make a hot water pastry, puff pastry, sugar crust pastry. They really, really do."

It turns out that "access to good content" is his biggest bugbear. "At the moment, after porn, the second most searched thing online is food. It's radically massive. Yet it hasn't got a platform. It hasn't got a standard. It's just a load of filthy shit in general. It's just a load of crap. And the sites growing most aggressively are not those of food lovers, they're a bunch of plop, they're venture capitalists who have just gone and illegally skimmed off a bunch of recipes they don't own.

"So when Billy from wherever who's never cooked before and is on a budget and has two kids and types in that he wants to make a soup or a curry, what comes up in the first 20 or 30 hits is a load of shit. What's the quality control? There isn't any. Now, I know every one of my recipes is tested six times in the business and twice outside the business so I know my quality control is high. I know that every recipe costs me two grand to test. And if I'm writing 400 a year, that's a lot of money. But just by being clever you can make all the recipes 10% lower in salt, that's easily done, 20%, that's easily done."

And yet. He needs to get to the top of Google's search terms. That's the goal. "I believe it has the capacity to make the difference to more than a billion people. That for me is really exciting. I know it sounds like what Bill Gates says, that he doesn't really want to work on anything unless it has the capacity to affect the lives of a billion people and I admit that line came from him, but I'm doing it sincerely." He is. But still, it's a tall order. An impossible order. I motion at the Jawbone wristband. How many hours sleep did you get last night? "Five." Is that average? "No, last week was three and a half. But that was a really bad week."

But then, as well as the 8,000 employees and the mission to change the world, he also has four young children who, his Instagram feed shows, he does manage to make time for: his life seems impossibly busy but there's still plenty of sepia-tinted shots of mop-topped children in leotards and wellies running around the idyllic garden at his weekend house in the Essex countryside. (The high-techery doesn't extend to them. He made headlines last year when he told an interviewer he'd banned his older daughters from Facebook.)

The interview has overrun and he has a cooking demonstration to go to. Does it ever worry you that it might all go a bit Gordon Ramsay?

"What do you mean?" That you build an empire and then it all implodes. He fell out with his father-in-law, didn't he, and then the business went a bit tits up. Are you afraid of that?

"Every day. The one brilliant thing I've done in 15 years is employ like-minded lovely people that will probably be better than me at lots of things. Do I worry about not running a healthy business but laying people off and then they can't afford an apartment? Every day. So, we're what you call big now, but it could just take some little thing to skew and it would change dramatically.

"But luckily," he says, "I don't know why, but luckily, I'm not a worrier. I'm a bubbler." He is. He's a bubbler. It's not a quite a word, not quite a sentence. The visitor from Mars probably won't get it but he's doing it his way and, for everyone's sake, you have to hope he pulls it off.