He wears his chef's whites like a day-old designer shirt, tucked into black jeans under a navy pinstripe apron.

And on his artfully ruffled hair, only styling wax: no starched white hat for him. He chomps on chunks of bread as he moves between stations in his busy open-plan kitchen and, even in the middle of a busy Tuesday lunch service, stops to wash a pot or two and to chop a bunch of parsley along the way.

Fresh ingredients are lined up on the front counter for everyone to see. Order slips are jammed into the rack above the Pass at a frightening speed as the pace picks up - two roast quail with hazelnut pesto, remoulade and foie gras for table one; four Jacob's ladder with root veg, lentils, capers and dill for table 10; three roast pork belly with butternut fondant, cime di rapa, pumpkin seed pesto and sage for table three. The pressure mounts, and I hear him swear several times, but directly into the ear of his chef, and not loudly enough to disturb the diners who can watch his every move from the comfort of the exquisitely designed front of house, where circular green leather banquettes and bright red chairs grouped around natural wood vintage tables glow in the dappled daylight coming from the glazed roof of this former Victorian warehouse, creating the moody ambience of an Edward Hopper painting.

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Except that Larbert-born Neil Borthwick is not set in aspic. He's a protege of Gordon Ramsay, yet when he uses the f-word to reprimand a chef de partie for letting a sauce get too hot, or when the kitchen porter can't find the leeks in the morning delivery, he does so with just enough vigour for the person to feel chastised but not blown out. "I believe in these guys, that's why I take the trouble to keep them right," he explains simply. "The Ramsay days of screaming and shouting are over."

Not what you might expect from the head chef of the Merchants' Tavern in Shoreditch, one of the most talked-about new restaurants in London. But then, if Borthwick's approach is collegiate rather than dictatorial, and low-key to the point of humble, his apparent insouciance belies a life of hard graft informed by the fundamentals of classical French cuisine, and powered by Sabatier-strength resolve.

His intensely seasonal food and its achingly pretty presentation is making its mark. Hard-to-please critics have variously declared themselves "enchanted" by his Scottish venison dish, bowled over by his "triumphant paeon to cabbage", and pleased by his "fetching" dish of Orkney scallops with crushed celeriac and black truffle vinaigrette. One even went so far as to declare, almost despite herself, that "clearly, Borthwick has unstoppable cooking talent".

At 32 he's become a major figure in the group of talented young chefs spearheading the new wave of brilliant British cooking, among whom momentum is gathering for the view that the famous Michelin restaurant guide is out of touch, and missing a trick by ignoring restaurants, brasseries and gastro-pubs that offer delicious, value for money dishes based on classical techniques.

"The Michelin Guide has amazing power, but I do think it needs a bit of revising," he says during a brief break. "There are guys out there serving fantastic food that don't get a look-in from the Michelin Star inspectors. They're not acknowledging what new chefs are doing because they are more focused on established names and reputations than the food on the plate.

"There are lots of good chefs coming through who are influenced by France through training with the Roux brothers, Pierre Kaufmann, Gordon Ramsay and so on, but their work is going virtually unnoticed. There's a new way of thinking in cooking right now that a meal should be about going back to basics, sitting down to make it a sharing occasion with family and friends. People want great food when they go out to eat. But Michelin is stuck on the molecular movement. I know I'd rather have three dishes that are delicious than wade through an 18-course tasting menu where three or four of the dishes might be all right." To emphasise his point, he cites with pride one critic who described his menu as "food that hugs you and puts a woolly scarf around your neck".

Borthwick, who was at Dollar Acadamy from the age of six and left at 17 with a couple of Highers, started as a potwasher at the Killearn Hotel when he was 14, and got his training there as commis chef under Ken McPhee. He worked for a year at Ramsay's Glasgow restaurant Amaryllis under the late head chef David Dempsey. He's the partner of Angela Hartnett, another Ramsay protegee who launched Amaryllis and made her name at The Connaught, Ramsay's Mayfair restaurant where she gained her first Michelin star. It was at The Connaught that she and Borthwick first met (he was sous-chef there on Dempsey's recommendation). She now has her own growing empire of Murano, Cafe Murano and, since October last year, Merchant's Tavern. It was she who appointed Borthwick to the top job. But the hotly competitive, financially risky restaurant business couldn't afford to rely on nepotism. Borthwick was appointed on merit.

While a 21-year-old HNC student of professional cookery and patisserie at Glenrothes College, he entered the Gordon Ramsay scholarship competition at the Glasgow College of Food Technology (now City of Glasgow College) with a dish he says was "shocking". It was to be Ramsay's own recipe for salmon fillet with tomato butter sauce. "I was given the most unripe cherry tomatoes I'd ever seen and I cooked a shocker, so obviously I didn't win the scholarship. But Gordon said, 'you should speak to David, and come to Amaryllis'." So that's what he did. After a year, in 2002, Dempsey helped him to get to Ramsay's restaurant at The Connaught.

Under Dempsey, Amaryllis gained a Michelin star in 2002, though Ramsay closed it in 2004 after the chef's tragic drug-related death, aged 31, in 2003. Ramsay caused a stir among the locals by announcing he was closing Amaryllis because there was no appetite for fine-dining in Glasgow (locals riposted that in fact the food was unfeasibly high-end and the ambience too formal).

Borthwick says now: "Amaryllis still wouldn't be right today. The food wasn't right. The chefs didn't have the commitment, and they couldn't see through the shouting that they could benefit hugely from the experience, and that they were being shouted at because they were worth investing in."

Borthwick stuck it out. "Amaryllis was fantastic, a real eye-opener. It was my first full-time job and I learned so much from David, using all these fantastic ingredients such as foie gras and Scottish scallops at such a young age. He was a real friend."

He'd been out with Dempsey in Chelsea a few hours before the chef died, but had gone home because he was working early next day at The Connaught, while Dempsey went on to meet with other friends. "Angela told me about David a couple of days later, and everyone was devastated."

Ramsay continued to invest in Borthwick. What does he think he saw in him? "I think he saw my passion, enthusiasm and commitment." But after three years at The Connaught he knew he needed to learn more. At the age of 25, he headed to the three-star La Maison Pic in Valence to work alongside Anne-Sophie Pic, France's top female chef. Then he loaded up his Peugeot, strapped on his bicycle, and drove over to Laguiole, Aveyron, to spend three years with Michel Bras at his three-Michelin star restaurant. That experience was the turning point for Borthwick - on a personal as well as professional level. Hartnett visited him frequently in France and it's where they became a couple. Also, Bras' skill in using local ingredients and foraged herbs and applying complex techniques to elevate them with often astonishing results was hugely influential.

During our conversation Borthwick frequently refers to "niac", Bras' word for something that shocks on the plate. For example, the Frenchman's starter of roasted onions has a "niac" of powdered black olives mixed with demerara sugar and ground almonds, which tastes like liquorice. I see something of this in Borthwick's sensational roast loin of venison, coated with a shiny slick of meltingly transparent lardo and paired with a deeply earthy beetroot puree with roast beetroot and wildly intense juniper crumbs.

It is like a taste explosion in the mouth; bold, fresh, youthful, exciting.

He says: "When Michel talked about niac, about lifting a mediocre dish into something really fantastic, I wanted to know how he did that. Too many young chefs don't bother.

"I'd work five double shifts from 7.30am or earlier, and not think twice about it. There was a lot more shouting back then, but you wanted to please the boss, to do things right and get praised for it. I thought nothing of sh*t jobs like working on 100 scallops, getting the green beans prepped and the girolles pickled, because you wanted to progress to doing the great stuff like the terrines. The best way to learn is to do the rubbish bits, because you get something from every job. I always enjoyed the energy in the kitchen no matter what I was doing." He worked his way up to sous-chef.

"Even the stagiaires (work experience) got to do proper tasks. I had to work with them and get them to work for me. If you didn't, you were in big trouble. Learning to delegate is a massive part of the job of head chef, and it's also the hardest part."

Is he enthused by the talent coming through? "The young guys here are handpicked. Too many use the internet for their information and they have no idea how to use ingredients.

"But not coming in to work, and making complaints, is much more common now than it was when I was younger. One chef de partie called in sick today, which made this morning extra tough, and three front of house staff have already complained at being shouted at. It's the people who take it, bow their heads and learn from it that will get on in this industry."

How does he get on with the boss? "Angela is logistical, organised, always giving us the benefit of her own experience and what she has learned." Her best trait? He laughs. "Bringing out the best in people, but at the same time having that spine of steel." His own best trait? "Getting on with people; you have to get on with everybody."

In fact, he's sociable and it was while cycling back, helmetless, from meeting a friend one afternoon last August that he sustained a severe knock to his head after falling off his bike. He was kept in a coma for five days and has had major surgery. He's wary about focusing on the incident, but he does say progress is ongoing and it's a matter of learning how to pace himself to build up his stamina. It was Hartnett, 45, who nursed him through the dark days. "Without her, I wouldn't be here doing what I'm doing. She has a nurturing personality."

What's it like going out with the boss? "People always say, 'Oh, you're going out with Angela Hartnett,' but I tell them, 'No, Angela's going out with me,'" he jokes. Just at that point, Hartnett walks in and reminds him sharply he's got a meeting to attend. The couple have just returned from a trip to the Holy Land for a celebration of Hartnett's grandmother's 80th birthday. Borthwick reveals he'd planned to take her to Italy to pop the question, but that he'll have to wait for another opportune moment when they're alone together. "We have discussed marriage on and off for years."

Borthwick's mother died of cancer when he was 20. He remains close to his sister Jennifer, who lives in Stockbridge, Edinburgh, and dotes on his one-year-old niece Holly. "Losing Mum changed everything. When your mum dies, the family home is not the same. There was nothing left for me in Scotland when she went. Since I couldn't go back to my own mum, I just went off and worked and worked, and didn't think twice. Cooking was my escape, my refuge, my way of grieving for her. I've never thought about that until now," he says. "I suppose my workmates became my new family."

As he packs up to join Hartnett for that all-important meeting, he adds: "I owe everything to Scotland and the mentors I met there. It has made me who I am." n

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