My meeting with Joanna MacGregor does not get off to a good start. "This place makes me lose the will to live," she sighs, glaring in a despairing way around the bar at the Lanesborough Hotel. The venue was my choice - she had suggested meeting at a noisy coffee shop down the road - and I should have known better. It is too chintzy, soulless and conventional for MacGregor, who has spent her career avoiding these adjectives.
With her plaited hair extensions and silver eyeliner, MacGregor maintains an appearance very deliberately not that of the typical classical pianist. In her work, too, she has refused to conform to the expectations of what she describes derisively as the "classical music establishment". One of Britain's most talented pianists, she specialises in Bach, but also champions left-field American composers such as John Cage, and collaborates with tango and jazz musicians, tabla players, DJs and film-makers. Her latest album, Moondog: sidewalk dances, is a tribute with the saxophonist Andy Sheppard to the eponymous American "outsider" composer, who was blind and lived rough on the streets of New York, dressed as a Viking. Live, MacGregor performs Moondog alongside Bach's Art of Fugue, and often - to squawks of protest from some critics - ventures to talk to the audience between works.
MacGregor describes her musical philosophy as "an equality of excellence", and it is showcased in the line-up for the forthcoming Bath Music Festival, which she has programmed for the second time this year. The classical big hitters such as Maxim Vengerov and the London Symphony Orchestra are there, but so are the Cuban son band Sierra Maestra and the gospel singer Mavis Staples. "It is about not conceding that some types of music are more important than others, which is an assumption that permeates musical culture," she explains. "They have to be excellent - that is all I ask of them."
It is an agenda that will make perfect sense to many music lovers. But, says MacGregor, it is still surprisingly controversial. "When I first came to Bath, some of the older concert-goers took one look at me and assumed I was going to destroy everything that they believed in - which is completely nuts, given that my career is based on playing some of the toughest pieces around in terms of the classical canon. They made an assumption that, because I had a love of other music, then somehow I couldn't have a substantial love and knowledge of classical music, too."
To a certain extent, MacGregor clearly relishes - and, indeed, encourages - the idea that she operates outside the classical mainstream, yet she also finds it both exasperating and personally hurtful that she is not completely accepted within it. The music critic Anthony Holden, who describes her as a "very exciting talent", acknowledges that in some quarters she provokes "misguided critical snobbery". "There is a certain exclusivity in classical music which has been very detrimental," says MacGregor. "People are made to feel that, if they want to be part of the classical world, they are not allowed to like anything else. Ironically, composers themselves - classical composers, let alone contem porary ones - invariably have a great love of many different kinds of music. Classical music turned into a club, and then found it had a dwindling membership."
She is, however, considerably more upbeat in her assessment of the future of classical music than some commentators - notably Norman Lebrecht, who mourned the decline of the clas sical recording industry in his recent book Maestros, Masterpieces and Madness. For MacGregor, the institutions may have failed to keep pace with a changing world, but the musicians themselves will always point the way forward.
"The problem with [Lebrecht's] argument is that his definition of great music is based on ideas which were current in 1945. He is wailing and moaning and gnashing his teeth, but musicians have already moved on.
"The classical music establishment wants to shut down, and repress, because it is feeling scared and on the defensive. A better reaction would be to open up and become a bit flexible, listen to musicians and hear what it is they want.
"It's a bit like colonialism, I think. When you feel that you've been at the centre of something, and suddenly you realise you are losing your grip on power, you lock yourself into the worst modes of behaviour. Instead, you could welcome the fact that you no longer have to carry the burden of being the cultural centre, and you could inject your position with new life."
MacGregor's identification with "outsider" musicians such as Moondog and his fellow American eccentric Conlon Nancarrow could seem affected: well-spoken, expensively dressed, and educated at Cambridge and the Royal Academy of Music in London, she is in many ways a product of the establishment. She did, however, also have an unusual upbringing, which she says gave her a sense that she "could never be the same as other people". Her father was a preacher at a predominantly black Seventh-Day Adventist church, and MacGregor did not attend school until the age of 11. She was introduced to music through gospel hymns and the piano lessons her mother gave her at home.
"I flourished very well by not being taught, because I was quite a solitary character with a strong inner world," she says. "It meant that I didn't get brainwashed too soon - my mother taught me all these different styles of music right from the start." She went on to have a normal adolescence, going to parties, hanging out with friends, and emphatically not practising the piano. "The traditional classical thing is that when they see a child has talent, the whip comes out. They're not allowed to play football, and they can't go to the school dance, and finally they get taken out of school because they're so special. I think it's awful."
Although MacGregor eventually moved away from formal religion, her Seventh-Day Adventist upbringing has left a permanent mark on her musical tastes and performance style. "What stays with you is this sense of being a preacher - in the best sense. It is not so much about God as it is about reaching out, communicating, and really having something to say. I took forward a great sense of passion and conviction from it."
If her live performances are any indication, MacGregor would have made an excellent evangelical preacher. With a combination of charisma and virtuosity, she persuades audiences to follow her on to territory they would never have anticipated exploring. I once went to see her perform at a very conservative venue on one of her Latin American tours. The programme was of the kind of contemporary music that is usually considered challenging - including one of Cage's works for "prepared piano", in which various implements are used to extract noises from an open instrument. Not only did the audience hang on her every note, but at the end it gave her a standing ovation. She nods when I mention this. "I have great faith in audiences."
I wonder to what extent the tide has already turned in favour of the kind of open-mindedness MacGregor advocates. The types of collaboration that she has pioneered are slowly being absorbed into the mainstream, with established classical companies including the Royal Ballet and English National Opera making efforts to bring in artists from other genres. "It has changed over the past 20 years," she concedes. "You do now have all the opera companies and string quartets and people who traditionally get the money reaching out a bit more. But often it goes horrifically wrong, like with [ENO's 2006 production] Gaddafi. You can't afford to get a project that wrong, as it gives companies the excuse not to try again for another decade."
The problem, she suggests, runs deeper than that. We are culturally still firmly rooted in an outdated definition of great musicianship. "Look at how few non-white musicians are actually doing the programming," she says. "They are just not coming up through the system - they operate on the outskirts. We have to bring into the centre different ways of music-making, different ways of composing, which aren't based on the classical model.
"It always feels like a struggle. You never feel like you've got there, ever. You are always clinging on by your fingers to the rock face."
The Bath International Music Festival 2007 runs at various venues from 18 May. More info: www.bathmusicfest.org.uk
1959 Born in Willesden, north-west London, to a piano teacher mother and printworker father
1978-81 MacGregor studies music at New Hall, Cambridge, under the British composer Hugh Wood. Completes her studies at the Royal Academy of Music and the Van Cliburn Piano Institute in Texas
1985 Selected for support by the Young Concert Artists Trust. A busy career as a touring musician with many of the world's leading orchestras begins
1990 Scripts a radio play, Memoirs of an Amnesiac, about the French composer Erik Satie, which is broadcast on the BBC. It is nominated for the Prix Italia
1998 Founds her own record label, SoundCircus
2002 Her eclectic album Play is nominated for the Mercury Music Prize. That same year, she makes her conducting debut with the Britten Sinfonia
2006 Appointed artistic director of the Bath International Music Festival"