Photography by Harry Borden
I approach in peace, which is a sensible starting point as John Vincent has barely sat down before he's standing up and offering me a demonstration of his martial arts.
'I'm learning Wing Tsun, which is a martial art first developed by women.' It involves: 'staying relaxed, recognising that most conflict is created by your own ego, never attacking but always hitting first ...'
He is a big man. Hold on, hitting first?
'Only if someone has begun to attack. I really wish I could show you,' he smiles. 'Come on, try and put me in an arm lock.'
Please don't hurt my right hand. 'Why, have you injured it?' No, I write with it. That's why I'm here.
For all the world, it looks like Vincent has forgotten. And that's his charm. Curly-haired, bedenimed, aged 45, he appears totally in thrall to his enthusiasms. Behind the toothy grin, however, he's also a smart organiser, trained at Procter & Gamble and Bain, and still an adviser to Vivian Imerman, the cash-hungry South African best-known for turning round Del Monte.
Somehow Vincent mixes all that with a voluble humour, a pugnacious interest in Eastern philosophies and a desire to make business a force for good. As he puts it, he likes to shake things up.
As co-founder of Leon, the healthy fast food chain, he has already done just that. The 12-year-old company, which sells coffee, juices, salads, meatballs and wraps - eat-in or take-away - now has 41 outlets, 750 staff and a £42m turnover, but punches well above its weight as a radical innovator in a ruthless marketplace.
'People copy us all the time,' he nods, 'superfood salads didn't exist before us, others didn't do hot wraps. When we launch a new menu we know M&S and Pret buy all our stuff, weigh it, cost it, decide what to copy.'
Doesn't that make him anxious? He shakes his head. 'It's like Wing Tsun, if someone is going to learn your martial art, you are always going to be better. It's the competitor that doesn't give a shit about Leon that worries me. We'll always stay ahead of the copiers.'
This summer he announced a ramping up of the Leon business, raising new finance to launch in America and promising to grow the London-centric chain to 500 branches in Britain and abroad. Why? Because you have to expand to keep good staff, he explains. And keeping employees happy is the reason why you are served with a smile - the single most noticeable change in Britain's food service scene. Two decades ago everyone was grumpy. Now nearly everyone beams. But only, says Vincent, if they like where they are working.
'The whole proposition at Leon is built around the wellbeing and happiness of the team. We treat them with kindness and love, and we track that, whether they are eating well, physically active, living in tune with the planet, learning and creating, free from toxins and stress, living with positivity and purpose ...'
His managers attend 'wellbeing' retreats twice a year at the Sussex country home he shares with his TV presenter wife Katie Derham. The timetable includes yoga, meditation, acupuncture and, of course, Wing Tsun.
And for critics who find this all too New Agey, he can translate. 'The way I want to lead is to be clear about the mission, find shit hot people, love them a lot, f***ing kick their arse if something goes wrong, then give them a hug.'
As for sceptics: 'I have my view based on results, they have theirs based on ignorance.'
He has a point. Leon's reputation is so high that he and co-founder Henry Dimbleby - whose father David, the veteran BBC newscaster, is a co-investor - were asked to lead a government-commissioned enquiry into school food three years ago. Both were awarded the MBE for services rendered.
And yet, given he swears like a trooper and dresses like Shakin' Stevens, Vincent isn't entering the Establishment just yet. Leon's head office remains a grungy hotchpotch of rooms up 80-odd stairs in a Victorian block beside London's bustling Borough Market. Old furniture, boxes of samples, and a large list of Abraham Lincoln's setbacks and reversals, painted on the wall, greet the visitor. The point about President Lincoln being, I guess, that persistence pays off in the end. It should add the final line '... and then you get shot'.
Vincent likes a joke. He talks with a chuckle and the very name of his business is steeped in humour and love, so-called after his own father, Leon Vincent, a cash register salesman from north London.
That insistence that business must be fun has echoes of another company too: that of Vincent's old friend Richard Reed, co-founder of Innocent, the smoothie brand. The two ran a clubbing business together at Cambridge University and you can sniff the competitiveness in their relationship.
Vincent cites Reed's success in setting up Innocent as key in his own decision to leave management consultancy, and he's typically forthright in describing their bond. 'I f***ing love Richard, he's brilliant and principled.' Reed, at time of writing, was uncontactable, climbing Mount Etna with Richard Branson, but given that he is godfather to Vincent's elder daughter, you can guess the love is reciprocated.
And just like Innocent, Leon has learnt from its difficult moments. Launched with a boost from the media celebrity connection, the chain grew then faltered, initially co-run by its founders, then just by Dimbleby, now - after losing money post-2008 - just by Vincent.
The two founders, who met at Bain, appear to have swapped roles without rancour. Both are foodies, both obsessed with detail, both culture-driven. But Dimbleby, now a non-executive, says that the plan for faster growth better suits his friend's skill set.
'The bigger an organisation gets, the more important it is to have a leader who likes to shake things up. And John is very ambitious, very positive, never cynical.'
Vincent also wanted more control after pumping extra money into the business. Since he stepped up, the business has accelerated, with two senior finance executives poached from Wagamama, new expansion plans announced, options for franchising explored - nine of the current 41 outlets are run by outside firms in travel hubs. More sites outside London are sought (only three so far of the 32 wholly owned). The energy is almost palpable.
But is healthy fast food the right vehicle? Isn't America a huge risk? And if Leon is successful, won't a not-so-healthy giant like McDonald's or Burger King (a former Bain client) simply make him an offer his investors cannot refuse? Even Innocent eventually sold out to Coca-Cola.
'Innocent had to sell because it had no outlets and needed distribution, and big companies offer more distribution. We won't need to,' says Vincent. 'Our outlets are a string of pearls.'
And he is prepared. Leon has already hired a former Burger King chief executive, Brad Blum, to advise on expansion into America. In the UK, it hired former McDonald's executive John Upton as its MD in April.
Won't that compromise the vision? Not at all, says Vincent. The original concept for Leon was 'if God did McDonald's', and the interior design is deliberately styled on an older incarnation of the burger chain - just offering healthier fare.
He's also brutally honest about his brief time advising Burger King while at Bain. 'That's where I realised I wanted to revolutionise fast food. Their attitude was that it was just about the money.'
And that is all linked into society's shortcutting of everything from our need for sex to our need for sugar. 'It's why we get so f***ing fat and unhappy.' He wants to reverse that.
So why did he get so driven? He laughs loudly, then cites his parents and his upbringing. Born an only child in Enfield, north London, his mother a teacher, his father a salesman and frustrated entrepreneur, he grew up in a close, loving family with English and Italian roots - his grandfather Giovanni Vincenzo Febraro, a hairdresser from Naples, anglicised the family name to Vincent during the Second World War.
'My father studied at the LSE in the early 60s, but his dad's death really affected him and instead of getting a really good job he ended up selling cash registers. He had kindness and a sense of humour, but was more introverted than me.'
His mother, on the other hand, was a much-loved primary school teacher renowned for her positive approach. 'Whatever happens she would say it's great. That positivity is key.'
They coached their son into being an exemplary student, outgoing and ambitious, who moved from state primary to private secondary school with ease. At Cambridge, he studied history but mostly, he jokes, he and Reed ran parties. 'They were like f***-you May Balls, because they wouldn't let me on the May Ball committee haha!'
Then came P&G, to earn money while he tried to get an entertainment company off the ground, and Bain, to earn more money for the same. 'P&G taught me process, and Bain strategy and finance.' Clients included Vodafone, Smith Group, De Beers and Burger King. Then escape with Dimbleby to launch Leon, while simultaneously working at Whyte & Mackay, the drinks firm, for Imerman. 'Schizoid, 100-hour weeks.'
Most of all, he just wanted to be his own boss. And now he is. But given the variety of his former interests, how can we be sure he'll stick? He's still listed as an adviser to Vasari, Imerman's buyout vehicle. He laughs that off. 'I love Vivian and Vivian loves me but we have separate bedrooms.'
Huh? 'It's a METAPHOR,' he shouts, giggling before getting serious. 'I was doing too many things before. Now, Leon is my passion.' Imerman also holds a 12% stake in Leon so why, adds Vincent, would he want to distract him?
James Allen, co-leader of Bain's global strategy practice and Vincent's former boss, says the biggest challenge facing the Leon CEO is patience. 'He has to solidify the platform of Leon before rapid expansion. John has a big brain and a big heart but that is almost bursting out of a small enterprise.'
And you can feel the ideas fizzing from Vincent when he speaks, citing books, therapies, art, politics, the threat of business to the planet. How does Leon's board ever keep him on track? Next he wants to assemble a panel of international advisers. After seeing me, he's off to Washington DC to scout for sites to open Leon there.
More prosaically, right now he has to change his shirt, as his assistant has vetoed the old one for the photoshoot. He pulls off one, drags on another, while pointing to the different Leon logos propped around the room. The late Wally Olins, brand guru, advised the launch.
'He was a mentor, but he hated all the corporate design rules he'd created. So we try and get away from the dead hand of the Mac. Here there is no one Leon logo, just a set of ideas ...'
And if nothing else, that name has a personal twist that is piquant. 'I think my father concluded that there were a lot of w***ers in business,' he chuckles. 'That makes me an avenger.'
THREE CHALLENGES FACING VINCENT
Finding new sites despite London's steep property costs
Managing the impact of Brexit on access to a young European workforce
Winning in the US without distraction from the UK market
VINCENT IN A MINUTE
1971: Born 28 September in Enfield, north London. Educated at Haberdashers' Aske's and Cambridge University
1993: Recruited by Procter & Gamble in sales and marketing
1997: Joins Bain as management consultant
2004: Co-leads turnaround team at Whyte & Mackay
2004: Sets up Leon with Henry Dimbleby
2008: Becomes non-exec at Leon
2012: Returns to executive role at Leon overseeing food
2014: Appointed CEO of Leon
2015: Awarded MBE with Dimbleby for work in improving school lunches.