Britain's leading baritone, Thomas Allen, grew up in a coal-mining town and started out singing around the piano. He was taken up by WNO, broke through with his Barber of Seville, became renowned for his Don Giovanni and is now playing Sweeney Todd in a production he hopes will encourage new audiences

Two years ago, Thomas Allen was being interviewed at the Royal Opera House in Covent Garden. As a member of the board, he was increasingly frustrated that high ticket prices were keeping too many people away from some of the finest opera on show anywhere in the world. Moving to the window of an anonymous office in the administration block, he pointed over the road to the Theatre Royal, Drury Lane. "People flocked there to see Miss Saigon," he said. "I went to see it and for the life of me I couldn't see why it was so popular. Madama Butterfly over here is a far superior piece with a great, great story, the most wonderful music and the best people singing it. What we've got to do is bridge that gap of 100 yards and get the coach parties arriving at Bow Street. Seat prices are going to be a part of that, but so is our determination and ability to continue putting on great work."

Roll forward to a few weeks ago and Allen, no longer a board member, is sitting in the same room, this time talking about his title role in a new production of Stephen Sondheim's 1979 musical, Sweeney Todd, which opens on December 15. A policy decision to move the mountain to Mohammed? "There may have been a bit of that," he laughs. "But if you are looking for something to represent a widening of the range here, then this is the leading candidate. You can't say the whole of the Sondheim canon would work. For instance I think Night Music might seem a little lightweight in comparison, but Sweeney Todd really holds together and has been a revelation in how much it repays investigation. It is a very rich, deep vein to mine and it is a measure of any good work that the more you delve into it, the more it gives. That said, I was hoping the top price seats would be a bit lower than they are [stalls are £75] but I do get the sense that people are coming who don't normally go to he opera."

Allen has been a leading figure in British musical life since the early 1970s and Gramophone magazine excitedly announced that here was "surely the best British lyric baritone singing in opera since the war". He has become renowned for his wide range of roles and recordings and is a draw in opera and as a recitalist across the world.

Jonathan Miller, who directed Allen in what became known as Covent Garden's "Armani" production of Cosi Fan Tutte, says: "There is something so deft and original in his presentation that he inspires those around him. He is always slightly different and fresh every night without being in any sense dangerously capricious and he has an enormous allure for the audience. Whenever he is on the stage the electrical potential goes up by several hundred volts. He is not only a wonderful artist, he is also a very important Englishman." Important enough for Allen to be knighted and granted a visiting professorship at Oxford.

He has also gained a public platform that he has used to promote increased access to the high arts while seeking to demolish the notion that audiences can be created by dumbing down. In a speech last year at the Royal Philharmonic Society's awards dinner, he claimed that "the idea of a wet T-shirted quartet, where once was the Amadeus, has me reaching for the seasick pills". He went on to castigate the South Bank's programming policy - too many performances of Beethoven's Fifth - and a machinery of hyperbole that "promotes the modest talents of a schoolgirl chanteuse or a pub tenor", but not more genuinely gifted and honed young talent.

This paper noted that "parts of his speech - the passages on Elgar, Shakespeare and the King James version - huffed and puffed a bit like a Private Eye letter from Sir Herbert Gusset". But Allen doesn't think what he said was particularly outrageous. "All I was saying was let us not fool ourselves that audiences are coming to us via amplified string quartets or the Opera Cuties or whatever they're called. That is a separate entity controlled by marketing to try to keep the recording industry's business going. I just want people to see opera for what it is. It doesn't need to be popularised. It is well able to stand on its own."

The tenor Robert Tear sang in Allen's first production at Covent Garden, Billy Budd, and more than three decades later they are again sharing the stage in Sweeney Todd. "Tom is basically a good working-class chap," says Tear. "In a way he is a natural socialist in that he is very democratic in rehearsals and despite his eminence doesn't pull rank on younger or less well-known singers. Likewise he feels very strongly about any slipping of standards. He really thinks the very best of our art should be there and available to anyone who wants it."

Thomas Boaz Allen - his grandfather, father and son all share the biblical middle name - was born in the Durham fishing village of Seaham Harbour in 1944. With nearly every male member of his family working at the local coal mine, he says there is no way of describing his childhood without it sounding like a Catherine Cookson novel. That said, the only child of Florence and Thomas Allen was an exception in the village in that his father didn't work at the mine and the family didn't live in a coal-board house. Tom Snr had escaped a career working at the pit after losing a leg in a motorcycle accident at 21. Instead he became the "never-never man", collecting HP payments for a Sunderland department store and eventually became their customer credit department manager.

After attending the local primary school, Allen passed the 11-plus and went to Ryhope Grammar School. "I think I am still in favour of the 11-plus," he says, "although I do recognise that it does separate children and I didn't really maintain contact with friends who didn't pass. But it did open doors for me and coming into contact with academic men who were Greek and Latin scholars, chemists and physicists and people who could speak French and German was extraordinary."

At school he became captain of his house and later head boy. He was a good athlete and a county standard golfer. "The golf club was full of pitmen and it wasn't seen as a particularly middle-class pursuit. I played with my father and we started off sharing a set of clubs, with me running across the fairway to get a club between each shot. He smashed three of his false legs playing golf but he loved playing it as it was his chance to get out into the open air."

Perhaps inevitably, music was the other ever-present childhood pastime. He says he could sing and harmonise as a small boy but steered clear of school plays. "I really wish I had done them now," he says. "But there was always something rather sissyfying about them and people would be ridiculed. Although for some reason singing was fine, perhaps because it was part of a male voice choral tradition."

His cousin, Edith Drennan, who lived with his family, says that "both his mam and his dad's family had some really good singers and I can remember Tom, aged five or six, standing by the piano singing 'Cockles and Mussels'. But the first inkling that his voice was special came when the music teacher at school suggested he should do a solo. He came home and said to his mother that he didn't want to do it. But she encouraged him to look through his dad's music and picked out 'Simon the Cellarer' [a Victorian parlour song]. He sang it at the concert and absolutely brought the place down."

Allen sings this on his latest recording, Songs My Father Taught Me (Hyperion) released earlier this year. School-friend Tom Connell, now a biology teacher, sang in the church choir with Allen and also remembers well that first school concert. "Of course his voice was very good, but what was almost more remarkable was that his acting talent was so obvious. He had very expressive gestures and manner and didn't just stand there and sing."

Allen began playing the organ in church and entered singing competitions all over the country. He abandoned his initial ambition to be a doctor and won a place at the Royal College of Music in 1964. "He was the first member of the family to go away to college," says Drennan. "But while we always knew he would make something of himself, although it wasn't what we expected."

Allen says he found life away from home "very difficult at first because of my close and cosseted background. I thought the college was just like some kind of finishing school and I felt like a square peg in a round hole. I was intimidated by the confidence of the people around me and used to ring my parents night after night saying I wanted to go home. It was absolutely pathetic, but I just wasn't prepared for it."

The pianist Roger Vignoles met Allen at college and went on to record with him and accompany him in recitals. "I'm sure when he arrived he did find everyone appallingly 'la-di-da'," he says. "But by the end he was the college star. He sang much more oratorio and song than opera but when there was a visit from the Queen Mother and the opera school needed an Escamillo for a presentation of the last act of Carmen, someone asked Tom. And he sang and acted everyone else off the stage."

Allen says the turning point came when he moved into a flat with some fellow students and began to get more comfortable socially as well as coming to the realisation that people wanted to listen to his voice. "My voice was really quite a natural one and I was generally involved in what I thought of as the rather pure study of lieder and oratorio. But then, towards the end of my course, I had a chance to study under James Lockhart, who was at Covent Garden. It was Jimmy who taught me some of the rules and regulations of the Italian language and how to mark up an operatic score."

Just as Allen was graduating in 1968, having been awarded the prestigious Queen's Prize, Lockhart became music director of the Welsh National Opera and suggested Allen audition. He was offered some understudy roles and made his debut in La Traviata in a school hall in Haverfordwest, Pembrokeshire. The following summer Allen joined the Glyndebourne chorus, winning a prize for choral singing. He found himself being able to choose between Cardiff and Sussex and remembers "being in the most awful dilemma. I worried that if I chose the wrong one, the other side would shun me for ever". But eventually he chose the WNO.

Lockhart says: "Although he was a greenhorn, Tom had stood out as a student. While you can never be absolutely sure with singers, I did have faith that he would develop. I could offer him the opportunity to sing both small roles in big theatres and big roles in small places. He was allowed to do his apprenticeship in these slightly out of the way places and he developed enormously in those years."

Allen's first title role came in 1969 in The Barber of Seville. The critic of Opera magazine showed some perception in picking out "a talent to watch" and noting that his "rich voice, and the kind of personality that seems to take productions naturally, added up to a blend of real promise".

By this time Allen had been married for a year to Margaret Holley. They had known each other since school and had one son, Stephen, a professional golfer. The marriage broke up in 1984 and they were divorced in 1987. The following year Allen married Jeannie Lascelles, a South African former model for Hardy Amies. He has two granddaughters and four step-granddaughters. "So the model railway has stayed in the loft," he laughs. "Although it has also meant Stephen never had the dilemma as to whether to call his son Boaz."

Allen enjoyed being part of a company at the WNO. "This is where I belonged, this was the real thing. I think it is because I am from such a strong community that I like being part of an artistic community."

He was first noticed in The Barber of Seville, but playing the role of Papageno in The Magic Flute was his first real milestone. "I know they had other ideas about who should play the part," he says, "but they had me on hand for 30 quid a week so they thought, 'why not?' After that they entrusted me with Papageno and after Papageno it was Billy Budd."

It was in Billy Budd, singing Donald, that Allen made his debut at Covent Garden in 1971. He joined the company the following year. Lockhart says: "It was no surprise when Covent Garden took him from us. We always knew that was going to happen and we were only glad that it was Covent Garden and he didn't move abroad." Tear remembers him arriving as an "amazingly gifted as well as a very percipient and intelligent singer. He had a lightness about him and could quickly see where things were going in a production and what a conductor or director wanted."

Over the next few years Covent Garden nurtured Allen in small roles with the occasional principal part. He began to build a reputation as a versatile singer and a commanding stage presence. In 1974 he sang in the premiere of Thea Musgrave's opera, The Voice of Ariadne, at the Aldeburgh Festival. Musgrave had not met him before rehearsals and remembers initially getting frustrated. "I was complaining about why this singer wasn't doing this and that," she recalls. "As the composer I wanted everything, right there in front of me at once. But I was advised to be a bit more patient and told that Tom was a good actor who needed time to digest things. I reluctantly agreed and then watched as Tom developed this character over time that was completely genuine and he was absolutely stunning in the part."

Miller goes so far as to say that Allen is among the best actors he has worked with. "I know there are now very few of those Jurassic Park singers who can't get from one side of the stage to another without assistance," he says. "But Tom is not good considering he is a singer, he is an outstandingly accomplished stage presence whether he is singing or not. He brings a subtlety and finesse that is almost unprecedented. I've often tried to persuade him to take non-speaking parts and think he'd be wonderful in Chekhov."

Allen, who reads poetry at some of his recitals, admits he "longs to" attempt a non-singing part. "I think that is quite well known, and while matching the time to the project might be difficult, I would make sure I had the time if something interesting came along. Part of the thrill of doing Sweeney Todd is certainly that there is both music and dialogue."

Despite this interest in non-musical acting, Allen characterises his habitual approach to career development as "small-c conservatism". In 1977, he turned down an offer to work with Herbert von Karajan on Il Trovatore. Allen cites the aphorism that all that is needed for a good Trovatore is to put the four greatest singers in the world on stage. "My instincts didn't point towards singing such a heavy Verdi role at that time," he says. Despite concerted pressure from Von Karajan's camp, Allen remained firm. "There were enough documented cases of people blowing their voice and I didn't want to even chance that. I was looking after a family and paying a mortgage and I wanted a long-term career."

But the mere fact of Von Karajan's interest confirmed that Allen was being elevated from the highly promising category into the real thing. Around the same time he recalls a number of Covent Garden productions in which, he says, "I really had to raise my game". These culminated with his Count Almaviva in the 1977 performances of Le Nozze di Figaro conducted by the Austrian legend Karl Böhm. "I know there was some reticence within Covent Garden about me singing the count," he says. "But as is so often the case, it was an outside party, Böhm, who recognised something in me. He was a great advocate for me and the confidence that came from someone such as Böhm showing such faith made me think that perhaps a freelance career was possible and so it proved to be."

Allen left the Covent Garden company and began to take up offers from other opera houses he had previously been refusing. In 1977 he also made his debut as Don Giovanni at Glyndebourne, conducted by Bernard Haitink. "Tom was already a theatre animal," says Haitink. "It was as if he had been born on stage. And that Don Giovanni was the highlight of my time at Glyndebourne. He completely claimed the role for himself and after working on that production it was always difficult for me to face other Don Giovannis."

Over the past few years Allen says he has received fewer offers to sing this signature role. "It doesn't exactly bug me, and I will be singing it in Germany next year," he says. "But it is one of those interesting roles that you might have more to say about as you get older. I saw Cesare Siepi singing it here, late in his career, and it was extraordinary. It wasn't a young man making his impact on the world. It was an imposing man with a lot of history behind him who was now rather more selective and more of a connoisseur. It stands up to that."

Allen made his debut at the Met in New York in 1981 as Papageno, by which time he was a fixture on the international circuit. His diary of his life on the road, Foreign Parts (1993), is, perhaps predictably, heavy on the hassles and deadening effect of near-constant travel. But it also provides an evocative insight into the creative process, such as his "euphoria" after a successful rehearsal for his role of Beckmesser in Wagner's Die Meistersinger von Nürnberg. "I'd never really gone out to fight for roles," he says, "but I did with Beckmesser. That opera was so important to me that I moved heaven and earth to be in it. But in the first few weeks of the rehearsal I thought I might have made a mistake. It was a very difficult transition from a role like, say, Don Giovanni and I really didn't know whether I could bring anything to it. But now I feel about Beckmesser the same as I do about Giovanni. I can walk on to the stage and just be him."

Haitink, who conducted the production, says Allen's Beckmesser was "unique in that he didn't make it a caricature. Usually he is an embarrassment and people tend to go over the top playing him. Of course Tom had some funny moments, but the undercurrent of the role was very genuine and moving. Here was an unhappy and frustrated man who couldn't find his way in life."

Another Covent Garden triumph, and another role Allen claimed as the representative of his generation, was as Don Alfonso in Miller's 1995 Cosi Fan Tutte. Allen made headlines when his character used a mobile phone on stage, but the critic Max Loppert described his performance as "simply astonishing", despite noting that Allen's baritone was no longer "quite the rounded, muscular instrument of 20 years ago". But as well as striding the international stage, Allen has been a long-standing ambassador for British song, particularly north-country folk songs. He says that just like track and field athletics, there are different forms of singing. "And my natural distance is British songs. They are where I belong. From the beginning I had a very natural voice that lay with homely, round-the-piano songs. It was the high art of most opera that I had to work hardest on."

The composer John Casken set the work of northern poets to music in a work called Still Mine, which Allen premiered at the 1992 Proms. "I think he was the only person able to really sing them from the inside," says Casken. "The major poem I used was John Silkin's 'Killhope Wheel'. Killhope is now a museum, but was once a working lead mine in Teesdale and Tom and I visited it. It's a terribly jargonised word now, but there was a sense of him 'owning' the poem and he knew exactly how to colour every line."

Along with his CBE in 1989 and knighthood 10 years later, Allen has taken on a series of "great and good" appointments. He is a popular president of the British Youth Opera and in 2000 was the Hambro visiting professor of opera studies at Oxford University, despite some muttering from members of the music faculty that Allen wasn't enough of a musicologist to be awarded the visiting chair. But Dr Michael Burden, fellow in opera studies at New College, who worked with Allen, says his lectures, master classes and performances were great successes. "He was very fluently and entertainingly able to express his wealth of experience to the students and audiences who were entertained as well as instructed."

And Allen is still keen to speak to a more general audience about the condition of serious musical endeavour in this country. "You can get a big crowd for Pavarotti in the Park or for the Three Tenors," he says. "But my guess is that not many of those people then go on to an opera house to hear the whole work. They go for the spectacle or to see the big man, and all that is fine. But it is not much to do with building an audience. What we should be doing is making the best opera and music we can available to more people. And that is made more difficult the more we go down the private money path and the more the government gives the appearance that it doesn't want to be too closely associated with high art forms. And I must say that I am particularly sad that this Labour government doesn't appear to be interested."

This commitment to excellence has never precluded him from singing the best popular works. At a Wigmore Hall Christmas concert in 1992, songs from Kiss Me Kate were followed by "White Christmas" and the entire audience joined in. He also paints, makes model ships, watches birds and plays golf and he directed a production of Britten's Albert Herring at the Royal College of Music last year. But most of all he sings and intends to keep doing so.

"In the last few years a couple of roles have come into my life which have been wonderful. There was Alfonso in Cosi, which is a wonderful psychological study as well as beautiful music to sing, and there was Beckmesser. And now there is Sweeney Todd, which has come as a wonderful surprise. It is such a refreshing and invigorating change to do something like this at this stage of one's career. And I sincerely hope that it is not only refreshing for me, but refreshing for this house and music in this country as well.

· Sweeney Todd: The Demon Barber of Fleet Street, directed by Neil Armfield with Paul Gemignani conducting, opens at the Royal Opera House on December 15 and plays until January 14

Thomas Boaz Allen

Born: September 10, 1944, Seaham Harbour, Co. Durham.

Education: 1955-64 Robert Richardson Grammar School, Ryhope; 1964-68 Royal College of Music.

Married: 1968 Margaret Holley (one son, Stephen) '86 divorced; '88 Jeannie Lascelles.

Career: 1969-72 Welsh National Opera; '72-78 Covent Garden company; '78- freelance singer.

Posts: 2000-1 Hambro visiting professor of opera, Oxford University; 2000- president of British Youth Opera.

Memoir: 1993 Foreign Parts.

Honours: 1984 Hon MA, Newcastle; '88 Hon DMus, Durham; '88 Fellow Royal College of Music; '89 CBE; '99 knighthood.