On a warm summer night, 30 years ago this week, Janet Baker made her last appearance in an opera. As she took her curtain calls after singing her final Orfeo in Gluck's Orfeo ed Euridice at Glyndebourne, a member of the chorus stepped forward and presented her with Orfeo's lyre, the instrument that had protected the character in the underworld by charming the furies, and now, it was hoped, would look after Dame Janet on her own journey into the unknown world of retirement.

The touching little ceremony was filmed and can be seen again as part of a reissued DVD/CD collection of Baker's work featuring a 1982 behind the scenes documentary, Full Circle, as well as the Glyndebourne Orfeo and an ENO production of another of her signature roles, Donizetti's Mary Stuart. "I used to be frightened of music frozen in a moment," she says now. "It was always so different to a live performance. But for someone in my age group, it is a relatively rare thing to be able to gather yourself together and this collection now represents a lifetime. I'm at a stage where most people have not seen me at work and so this feels like a very intimate and relevant thing to do."

Baker has recently been spending a lot of time looking back. "The lifetime award from Gramophone last year provoked the same emotions. And now, at last, I think I can listen objectively to my recordings and, for the most part, the span of my work has been a pleasant surprise. I'm much kinder about myself than I used to be."

It might have taken Baker some time to enjoy the fruits of her own career, but for everyone else she has long been regarded as one of the greatest ever British singers. Emerging in the mid-1950s she was seen as the natural heir to the great contralto Kathleen Ferrier who had died aged just 41 in 1953. By the late 50s and early 60s Baker was a leading figure in the baroque revival, singing Handel, Purcell and Monteverdi. In the 60s she became closely associated with Benjamin Britten and went on to have huge success on the opera and recital stages in both the UK and America. The director Peter Hall, with whom she often worked, said when presenting her with the Gramophone award that "she brought true human reality to something that can so easily become artificial". Bernard Levin was only half joking when he claimed that "no man may call himself fully civilised if he misses an opportunity to hear Janet Baker sing".

Baker was only 49 when she retired from the stage, and although she did continue to sing recitals for another seven years, there has long been a feeling that she left too soon. "It's a very personal thing," she says. "Someone like Placido will work to the end, but that wasn't for me. It has been suggested that retiring was a cop-out, but it was nothing of the kind. It is simply a fact of the amount of personal energy you were born with. My work always took everything out of me and there comes a time when you just don't ping back so fast."

Another factor was the way Baker regarded her own talent. "I always thought of it as a gift implanted in me, from wherever you choose to believe. It sort of worked separately, almost outside of me, and guided my life like a lodestone or magnetic north. In that sense the relinquishing of my public life was a little easier because I didn't want to let down the talent, this gift which had not only been such a joy, but had also been at times a quite heavy responsibility."

Baker says that it was only comparatively late in her career that she really began to enjoy performing "in a way that a lot of my colleagues did naturally. I was always very envious of this. To me it was torture. Not the performing itself, but getting geared up to do it. That 10 yards from the wings to the centre of the stage is a terrifying journey. But the only way you can sleep at night is to know that you have worked your tail off and given yourself the best chance of doing justice to whatever talent you have been blessed with."

She says even today at a concert she instinctively puts herself in the performer's shoes rather than those of a member of the audience. "My heart goes out to them because I know what the cost has been and it brings back quite a lot of vulnerability. That's why I go more to instrumental music than vocal music these days. I do find it slightly painful to sit and listen to my own repertoire and have not once listened to the Matthew Passion since I was no longer able to sing it. I know it's ridiculous to get butterflies on other people's behalf, but it was a part of my life for so long that I suppose it'll never go away."

Baker was born in Yorkshire in 1933. Although taken to both the theatre and ballet, there was little music in the house. "I shouldn't laugh," she laughs, "but my father was in the police choir and I used to go with him to concerts, all the time squirming in my seat as I knew this wasn't quite the music I wanted to listen to. I've got more sense now and have quite a soft spot for male voice choirs. But at age 10 I knew it wasn't good enough in the same way that I knew that singing a Bach chorale in church was. I must have been born with some sort of inbuilt quality control because there was no sense of that at home."

Although obviously a talented singer who won local competitions, there was little prospect of Baker going to music college and instead she got a job in a bank after leaving school and sang in the evenings. Then, after a performance of Haydn's "Nelson" Mass at York Minster in 1953 with the Leeds Philharmonic choir, in which Baker was given a small solo role alongside a professional soprano, Ilse Wolf, Wolf gave Baker the number of her teacher in London.

"On the train going home, our conductor, very ill advisedly, said I should definitely take it up as a career. That was all I needed and I told my parents I was going to London. The conductor actually came round to our house to apologise to my mother because he felt responsible for me making this rash decision. But despite them knowing nothing about a career in music, my parents let me go. That was extremely brave of them."

Baker secured a transfer to a London branch of the bank and contacted Wolf's teacher, Helene Isepp, who took her on as a pupil – Isepp's son, Martin, would later become Baker's regular accompanist. From that moment, Baker was introduced into a world of émigré intellectuals and musicians who had escaped from Hitler's Europe. "It was an incredible eye-opener, a very sophisticated, and sometimes daunting, world. Yet it was something that made sense. Not only did I now have a German-speaking singing teacher, but these people were feeding the whole arts community at that time and I was lucky to find myself among them."

In 1955 Baker joined the Ambrosian Singers, "who are forgotten now, but really were a crack team. We would just pick anything up and sing it for a live broadcast. It was quite a training." The following year she came second in the Kathleen Ferrier Memorial singing competition at the Wigmore Hall – cementing a perceived link with Ferrier that would last throughout her career although the two women never met – and made her debut with the Glyndebourne chorus.

The Ferrier prize brought her to the attention of a leading agent and soon Baker was singing principal roles. She says she was aware that she was a better singer than most of her colleagues in choirs in Yorkshire. But singing professionally "I was always standing next to people with voices easily as good as mine. And I did think it was strange why they had not gone on to try to make a name for themselves. The reason was that circumstance had stopped them. Getting married, having children, all the other responsibilities that come along. I wanted to be free to take risks and so while I did get married" – in 1957 she married Keith Shelley who become her business manager and who has been her "greatest support" ever since – "we chose not to have children because I knew, energy wise, I couldn't both bring up children and have a career. And that has never been a decision I have regretted. I realise that half of life is children, but I've had other things that have fulfilled me and I was very grateful that my circumstances did not trap me."

Success came quickly with starring roles at Aldeburgh, Glyndebourne and Covent Garden as well as acclaimed recitals of Mahler, Schubert, Elgar – her Angel from The Dream of Gerontius another echo of Ferrier – as well as Mozart and French song. How did she respond to stardom? "There is a moral question here. If you are doing it because you want people to love you then you should forget it. It doesn't work. If love and acclaim come as a bonus from doing good work then that is wonderful. There are few better feelings in the world, but you have to start with the work."

In New York speaking to the line of well-wishers after her annual concert at Carnegie Hall could take longer than the concert itself. "There were some who spoke to me briefly, asked me to sign a record and said 'Thank you, goodnight, see you next year.' That was smashing. But there were others who somehow want to get into your life. They wanted to think that they owned a bit of you. I had fans who followed me all over the world. That group thought they had a special relationship with me, but they did not. I was very grateful for their support, but also concerned not to allow myself to be taken over. I realise this sort of thing is nothing compared to the pop world, but I was wary of those people for whom the performer came before the music."

And in her own dealings with the great musical figures she says she retained a certain distance. "I was very aware that I was moving in different circles. Benjamin Britten? Dietrich Fischer-Dieskau?" She slightly chokes up remembering her friend Fischer-Dieskau who died in May. "A great colleague who was funny and warm and humorous, but I never forgot I was singing with Fischer-Dieskau. He was a very great man. Equally there is a respect and awe that never really leaves when you work with someone like Ben. And if you overstepped the mark you were finished with him. He had to create some distance or the poor man would have been swallowed by the world. People wanted to own him, so maybe that was something that I could appreciate and we had a friendship until the day he died."

Baker's long association with Britten took in his Aldeburgh festival as well as her 1966 Royal Opera House debut in his Midsummer Night's Dream. He wrote two roles specifically for Baker. In his 1970 opera written for television, Owen Wingrave, she sang the part of Kate and shortly before his death he wrote the solo cantata Phaedre for her. The role of the heartlessly cruel Kate brought Baker a certain notoriety. "Ben was very careful to explain to me what would happen when it was broadcast on television. He thought it would be tough for me and he was quite right. People seized on the fact that she was the nasty bitch. It was quite difficult and people still mention it. But as he said to me: 'You're an actress. Act it.'"

Observing other people asking Britten to write for them "made my hair stand on end. I never asked him, but his gift to me before he died was Phaedre. And that was wonderful. I'm sure it was his way of saying 'we have worked a lifetime together, so thank you'."

Baker enjoyed another special privilege from Britten in that he tolerated her working at Glyndebourne during a period of considerable antagonism between the Glyndebourne and Aldeburgh festivals. "Ben did like to come first. He thought if he wanted you at Aldeburgh then you should down tools anywhere else. I was never going to do that. I wasn't going to give up Glyndebourne and I wasn't going to give up Ben."

After ending her stage career at Glyndebourne, Baker continued to perform as a recitalist. "The mezzo roles in the opera house are wonderful in many ways, but on their own they are just not musically satisfying. Opera made up about a third of my life and so did recording, but I couldn't have lived without the concert repertoire as well."

She explains that there is "one less layer" between the singer and audience in a recital. "You are responsible for everything. You are the guide and whether the audience follows is solely down to you. The music emerges from a place in your gut that is completely your idea of how to serve the composer and the poet so there is no hiding place. You hold something very precious in your hands for two hours and God help you if you drop it."

While she says she doesn't miss performing, she does miss working with other artists. After recently attending Covent Garden to celebrate director John Copley's 50 years at the house she says "in the auditorium I felt completely at home and that I had never left the business. But when we were cutting the birthday cake for John on stage, I felt like a total outsider. With the best will in the world, you just don't belong there anymore. There is a very subtle dividing line between those who are still doing it and those who are not."

Following the end of her performing career Baker has taken up a number of positions, most notably as a long-standing chancellor of the University of York and a patron of the Leeds piano competition. But she says that her work as a singer in a way prepared her for retirement. In a 1967 interview she revealed that she was reading Jung. "The stuff of performing has to be very much an interior journey," she says now. "You have to understand an awful lot of what is going on inside yourself. My interest in what makes a human being function was applied to roles, but has also been part of something that helps me in my retirement.

"You get absorbed by a job, you retire from it, and then, if you're lucky, there is this period of preparing to die if you like, a very interesting stage of life in itself. People say how lucky you are to have a gift, although what you do with that gift it has nothing to do with luck. But the really great thing is that it clarifies your life. Most people have to experiment with lots of different things with greater or lesser levels of satisfaction. So it has been a huge simplification of life to know that you are on the right path as both a performer and now as a retired performer. I've always trusted that there is a purpose to my life."