It would be easy to cast Nick Williams as a kingmaker: a second Simon Cowell, albeit with a smaller office, smaller hair and no visible entourage of 1980s pop stars. If he were to appear on a television talent show, he would doubtless be described in booming voiceover as the mastermind behind megastars Adele, Jessie J and Amy Winehouse.
This is not, however, how he sees himself. "Take Adele and Jessie J (pictured, right)," he says. "Yes, they were undoubtedly talented. But did they come across as the most talented people we knew? No.
"Some people leave and I've thought, 'you're going to be very, very successful', and they haven't been. And some people go on and are very successful and you think, 'how did that happen?'"
Williams is the retiring principal of the Brit School, Britain's first state school for the performing arts. During his decade in charge, the school has famously produced many of the most successful singers of recent years. Alongside Adele, Brit alumni Leona Lewis and Katie Melua make up three-quarters of the 2012 The Sunday Times' top-four highest-earning pop singers under the age of 30. Winehouse appeared on the rich list in previous years.
But Williams is extremely unlikely to appear on a TV talent show. His school is not, and has never been, intended as an instant route to fame. Instead, it prepares pupils for careers in all aspects of the creative industries, from performance to film-making and stage management to set construction.
During his years as principal, Williams has developed a keen understanding of the unpredictability of the industry. "The time was right for Adele and Jessie J, and the particular type of music they produce," he explains. "And both those students were very determined. Both lively, friendly, gregarious individuals; both charming individuals. And both have had luck - things have gone their way. They've sought out good support and they've been well managed. All those things have to come together for success, and that you can't predict."
He arrived at the school in 2002, after five-and-a-half years as head of south London's high-achieving Thomas Tallis School. At the time, he says, the Brit School was in chaos: failing academically and achieving surprisingly little, even in the arts.
"There were only about 17 music students in Year 12," he recalls. "And you're thinking: 'What? This is supposed to be the thing that the school is known for.'
"There were random opportunities for young people to engage creatively in the arts. But there was no connectedness between different aspects of the school," he says, adding: "We've got this opportunity to select students, so we should simply be the best - better than anybody else."
This very selectiveness, however, did make him doubt briefly whether he wanted the job. "I came from the classic NUT position, that local authorities should always run schools," he says. "Coming here was very challenging in that regard.
"But it's very hard, if you're a talented dancer or musical-theatre musician, to see a route into the upper echelons of those industries. You're competing against people who have often been privately taught since the age of four. It's rare that a state school can give the time, focus or pedagogy that provides a route for those who have decided that this is the right industry for them. We have something you don't get anywhere else. And that was my road to Damascus, really."
Williams barely pauses for breath before adding: "But I wouldn't have the same argument for grammar schools. They just perpetuate social inequalities."
In fact, the Brit School does not simply select its pupils: it auditions them. Williams acknowledges that there have been occasional auditionees who treat the process like a Big Brother application, showing off their far-out wackiness. Very occasionally, staff do this as well. "But I think we're well-enough known now," he says. "People know what to expect."
What you expect is, very much, what you get. On an overcast Monday afternoon, a group of pupils sits cross-legged on the lawn. One girl has pink hair; another, her own hair dyed a virulent magenta, walks past with a guitar case on her back. In a classroom nearby, two teenagers - one in a catsuit - are tap-dancing in front of a mirror. Across the hallway, a group of pupils with electric guitars are practising a self-penned musical. "It's the aftermath of the Jack and Jill story, set in East London," one of the musicians says. "It's exploring issues of mental illness."
Williams makes his own token gestures at sartorial creativity: along with his suit, he wears a red, blue and grey striped shirt with a similarly coloured spotted tie. One might almost be tempted to draw conclusions about his own frustrated artistry. "Yeah, undoubtedly," he admits. "I'd be interested in film-making, actually. I really love the whole media side of things. If I have any regret, it's that I never developed the skills or confidence for any of this."
A child of the 1960s, Williams came of professional age in the freewheeling 1970s. His first teaching job, in 1976, was at an inner-city school in Battersea, south-west London. "As a teacher, I've always been chancy, experimental," he says. "The lack of accountability back then meant it was a great time for slackers. So I'm not holding it up as the greatest time in education. Except that, if you were interested in innovation, you could do what you wanted. Particularly if your results were good."
Avant-garde is mostly the preserve of education's old guard now. But Williams insists that all schools would do well to follow in the Brit School's tap-dancing footsteps. "Some schools worry about giving young people too much freedom. The secret is to show that you can give them freedom, but that at the same time they can be very disciplined. The key is self-discipline."
If you walk into any Brit classroom, he says - even the academic ones - it will be rare to find pupils misbehaving. "I'm not saying that every single person who comes to the Brit School loves maths or loves science. Sometimes they don't even love their arts subject. But there's something about being able to pursue their creativity. They see school as a place that allows them to do what they want."
Confronted with proposals for the Brit School, Margaret Thatcher allegedly said: "Why do I want to create a school for unemployed artists?" But, says Williams, there are more jobs in the creative industries than in any other sector, except for finance. "It is a hard place to be," he acknowledges. "If you want to be sure about a profession, don't choose the arts. But, these days, what is secure? What do you do with a history degree?
"You come here because you want to be a choreographer, because you love being on stage, because you love painting. If you can make a living at it, even better. But even if they go off and become accountants, they'll always have that bit that's special to them. It's not just about earning a living."
Part of the Brit School's role in preparing pupils for the whims and vicissitudes of the creative industries involves teaching them to cope with failure. Williams quotes the playwright Samuel Beckett: "Try again. Fail again. Fail better."
"The school system has to be free enough to allow those chances to be taken," he says. "Classrooms are experimental places. The best teaching is provisional: ideas are explored. It's an experiment between the teachers and the students in the room. To be successful, you've got to take risks."
Risks he has taken in his decade at the Brit School include the decision to take 35 pupils to perform at the Glastonbury Festival. For six days, pupils and teachers lived in mud-logged tents. "People didn't believe that we did it, and performed to thousands of people," he says. "Two years in a row."
At Thomas Tallis, too, there were risks to be taken. Williams recalls standing at the school gates, dealing with the negative effects of the area's pervasive gang culture. "It makes most things pale into insignificance," is all he will say by way of detail. "Not being prepared to back down to keep your school safe. That's as challenging as anything you're going to face.
"I've taught in inner London for a long time, so I know how tough schools can be. That's something to throw back at people who say, 'you don't know the real world'. Before I came here, I was very much working in the real world. And this is just a different kind of real world."
The particular kind of reality that Brit kids inhabit was driven home forcefully last summer, with Winehouse's death from alcohol poisoning. "As a generalisation, it's true that creative people can often be prone to swings in their feelings and their emotions," Williams says. "Because they're more open, possibly less guarded, more risk-taking. And every now and then, events like Amy's death bring that home to people."
He regularly invites people from the industry - often Brit alumni themselves - to talk to pupils about their negotiation of the emotional difficulties involved. "It's about having conversations that are profound enough for young people to take them seriously," he says.
Brit's alumni - in all aspects of the industry - are a real strength of the school, and one that Williams is particularly keen to capitalise on: "They know the jobs that are out there, the skills you need. And they will have those skills."
But he insists that his doors are open to all former pupils, whether or not they have been successful in their chosen field. He discloses that quite a few come back in their mid-twenties to ask for advice on a faltering career. "One of the things that young people need to understand is that the chance of becoming a professional actor, even if you're very good, is very slim. So we need to develop resilience to the idea that they might get to the age of 30 and say, 'now is the time to quit'."
Or, indeed, get to the age of 58 and say it. "It's time to do something different," he says of his own retirement. "The key is to know it before anyone else knows it."
This year has been significant for Williams in a number of ways. He has just negotiated permission from the local council to expand the school, allowing for an extra 300 pupils over the next five years. He has launched a foundation degree course, accredited by Bournemouth University. He has conceived - and worked with the government to open - another performing-arts state school, this time in Birmingham. And he has worked with the local authority to open an associated primary school next to the Brit School.
"That's about seeing what creativity can look like in four-, five- and six-year-olds," he says. "Of course, you can't make them creative. Everybody's different. But in my own educational experience, at a very traditional grammar school, opportunities were actively closed down for me. It's a nature-nurture balance, but you can open young people's minds to the possibilities of creativity.
"Running a school has to be thoughtful. It involves thinking outside the boundaries and risk-taking and fear of failure - absolutely all the things that you do in the arts. In some ways, I see it as an art form."