When the ample Catalan sings: Callas is no more; Kiri Te Kanawa is making television commercials, but Montserrat Caballe, the 61-year-old soprano with the old-fashioned style, is still the people's diva of choice

WHAT DOES it take to be a diva? Not just some slip of a thing who can hit a top C, but a full-blown, Guinness-dark, D-I-V-A diva? I was asking myself that when I came upon a huge burgundy Bentley with the boot wide open. The courtesy car laid on for Montserrat Caballe during her stay in London was already full, and fitting in the two extra suitcases left behind in the hotel was proving to be something of a problem. The chauffeur was just taking a moment off to wipe his brow with a handkerchief.

The Catalan soprano had been on a flying visit to the capital to shop (with her husband, her daughter and her niece who doubles up as secretary), and to christen a new Channel Tunnel train that will bear her name. 'Zo zweet,' she described the ceremony in Calais. 'How wunnerful it will be fo' de two nations to hab de toon-el under de Channel]'

Caballe mixes English, Spanish, German and what I suppose must be Catalan with a complete disregard for accent or grammar. To transcribe her speech phonetically is not to mock her. It's just that without it, it's not her.

She was also in London to do a quick recce of the palace at Hampton Court, where she will be singing before the Prince of Wales on the last night of the festival next month. At 61, she may have reached an age when most of her peers have stopped singing professionally, but to many hers remains the sweetest voice of all, and the performance is virtually sold out.

Caballe is one of the last of the true divas. Callas is dead, Kiri Te Kanawa is busy making commercials for Sainsbury's, and Mirella Freni has never really risen out of the narrow confines of being an opera lover's opera-singer. Caballe, on the other hand, has always had an enormous following, and it's still with her today.

Thirty-six years after her debut, when the fashion in opera is for in-your-face reality, and when singers aren't afraid of being coarse or raucous or violent if the drama demands it, Caballe is still incapable of singing an ugly note. The essence of her appeal is a tone so sensuously warm, so beguiling, that it is just as entrancing at a pianissimo thread as when unfurled at full voice. But it is not really because of her pre-eminence as an opera star that she has become a household name. It is also due to the fact that she is generous and humorous enough, despite her devotion to bel canto, to have partnered Freddie Mercury in making an incredibly camp pop video - and really enjoyed it. 'Wid Freddie, that was an experience I never haf had before. It was a free worl' of music together.'

After the video, they recorded the song that became the Olympic anthem, Barcelona. While making the recording, four years before he died, the lead singer for Queen told her what he had never admitted publicly: that he had Aids. 'I think it was a way to show to me his frien'ship. It was a bery honourable thing to do. Yes. And bery bery brave.' Mercury died before they could perform at the opening of the Olympic Games. Caballe now sings around the world to raise funds for Aids research, for Unesco, Unicef, Amnesty International and for 'peace between de nations'.

When I asked her what it felt like to be a genuine diva - what kind of personality it took - Caballe seemed quite mystified and looked about her as if for an imaginary interpreter. 'No, I don' feel like a diva,' she said eventually in a tiny voice, trying to evade the question altogether.

She is very short - less than 5ft tall even in heels - yet also immensely broad. Her hair is dyed as black as tar, and teased into a huge helmet with a jaunty flick. She wore black chiffon, although it was mid-afternoon. Perhaps that is her secret. Or perhaps it is the diamonds, set in little trellised baskets of gold at her fingers and lobes. Or the swirling gold 'M' the size of her hand pinned to her midriff. Or is it what lay amply displayed and covered in fresh talcum powder, between the lapels of her jacket - between those apricot-coloured triangles aimed like jet fighter planes down her chest? Could it be that it is the diva's cleavage that makes the diva a diva?

I didn't ask that directly. 'I don' feel like a diva,' she repeated. 'I feel like a person who has dedicate' his whole life to the music I luff. Trying to serve the music the better I could, and to giff the public the woice that was born with me.'

The notion of the singer as slave to the music is hardly a new one, but with Caballe it's a sort of anthem. 'I am an ambassador. A sort of ambassador transmitting the news the composer wanted to tell the audience, and that is a sort of servant . . . (To bear a message) from another human being that is no more derr, and canno' tell you, you haff done wrrong or you haff done rright; is a big responsibility. Is a sort of miracle.'

MONTSERRAT CABALLE has always regarded her voice as a gift from God, and her role as that of a Messianic interpreter entrusted with a precious task. Like the archangel Gabriel, she has a job to do down here.

She was born into a strict Catholic family on 12 April 1933, and named in honour of the Black Virgin of Montserrat, patroness of Barcelona, her native city. She began singing along to her father's opera records at the age of five, but did not begin taking opera classes until she was 14. Two years later, she almost abandoned her studies after her father had to stop working because of heart trouble and she felt she should become the chief breadwinner of the family.

On the advice of the director of the Barcelona conservatory, she wrote to the Bertran family, who were known for their patronage of the arts in the city, and soon received an offer to fund all her studies and living expenses. The Bertrans paid for lessons in singing, theory of music and harmony, German and Italian. Their investment paid off and Caballe graduated at the top of her year. But she was so nervous performing that she was advised by an agent in Rome to give up, go home and find a husband instead.

When she finally married, at 29, it was to a fellow Catalan and singer, the tenor Bernabe Marti. During a performance of Madama Butterfly, Marti kissed her full on the lips during the love duet in the first act. She had never been kissed before. 'Dat was it,' she said. They married soon after.

She is still a strong, rather than strict, Catholic, and says she prays in the theatre or in hotel rooms more often than in church. The Martis eventually had two children, a son named Bernabe Junior and another Montserrat, a daughter, but Caballe never stopped singing. She ignored the Rome agent's miserable advice and made her professional debut as Mimi in La Boheme in 1957. She became one of the most sought-after sopranos in Europe, and later in the US when, one evening in 1965, she stepped in for an ailing mezzo-soprano at Carnegie Hall and took New York by storm as Lucrezia Borgia.

In an age when performers, artists and writers are often created by marketeers in search of a commodity, there is a simple, central truth about Montserrat Caballe: she possesses a soprano voice that, if we are lucky, comes once in a generation. It is true that her size and age inhibit her movements on stage, and that she often resembles a fine singing cupboard. But what a cupboard. What a voice. If you want a taste of what is so special about Caballe's singing, listen to her in the principal aria of Bellini's Norma, 'Casta diva'. It was the first thing I ever heard her sing, in a concert performance of the opera, and I have never forgotten it.

Most great singers feel themselves to be part of some great mystery in which they have been chosen, quite arbitrarily, to receive a startling gift. Caballe, whose gifts are more prodigious than most, is no exception. 'Everyone of us has a special thing when we are born. So in me this soun' was born with me. To develop that, first I loved the music, second I was devote' to the music. It's a way to say thank you fo' that wunnerful gift. Because not everyone has this chance.'

A gift it surely is, but it is also enormously hard work. Caballe lives in Vienna, but is rarely in any one place for more than a month. Her husband runs the family farm in Catalonia, and commutes between Vienna and Barcelona. She gets up at 3.30am. 'Is ahlways been so.'

She studies from 4am until 9am, rehearses through the morning and works on her correspondence in the afternoon. One of her abiding interests is new music - not contemporary so much as new discoveries from old composers - and in the evening this is what she will work on with her pianist. She travels with her niece Monty, who acts as her secretary and, occasionally, with her husband. If she is not performing, they will eat lightly and sometimes go to a concert. 'Otherwise, we remain in the hotels, watch the television and go to the bed.'

It isn't how one imagines a diva lives, but Caballe's dedication has, at least, fuelled a successful search for new roles. Too many opera stars stick to the repertoire they learnt at an early age, but find as they grow older that it suits them less and less well. Caballe has sung 132 roles on stage, and she is still learning new ones. Her old favourites include Strauss's Salome, which she sang for the first time in 1959 and still performs in concert.

'Richard Strauss, he is the las' o' de romanticos. I always say that. This Salome, she is so complex. Musically, it is so well described: the child woman, the bad child, the bad woman, the killing one, the malicious one. Dis is one of my favourites.' So are Norma, Rossini's Semiramide, and Isolde, which she embarked on only in 1989.

Caballe knows the value of learning new roles, and marshals her arguments briskly when it is suggested she may be past her best. 'Of course, from 25 to 40 are the bes' years for a singer. But there are the roles which I coul' not sung in these years. Like Medea. I was not the voice o' Medea in that time. Medea needs darker sound, brighter sound. Medea don' need the high soun'of a Traviata or a Norma, but needs a major workin' soun'.'

She will be touring Greece this summer to sing Cherubini's Medea in its true cities - in Corinth, in Delphi, at the Acropolis in Athens, and perhaps also at Epidaurus. And for next season she is learning Donizetti's Rosamunda d'Inghilterra. 'Rosamunda is a 50-year-old woman. You need a differen' kind of soun'. I will never sing in these days what belongs to young people. I will always do my repertoire with my age, because I think otherwise I will have betrayed myself, betrayed the composer, betrayed the audience. And this we cannot do.'

Drive, determination, discipline. They too are all part of Caballe's repertoire. And so we came to the element she feels most vehemently about: the importance of technik]

Any discussion of technique turns Caballe from a joyful romantic into a veritable matron. She wags her finger as she extols the virtues of a fine technical training, and the lazy way in which singers today try to do without the discipline it entails.

Sitting up suddenly erect in her chair, she became quite agitated. Her hands fluttered about her chest as she dissected the architecture of sound and explained the importance of supporting the diaphragm ('de deea-pragma'). She recalled taking a masterclass of 500 young singers in Madrid.

'I say to them. Firs' of all you have to have the soun'. Small, big, beautiful, not so beautiful. This you have to have if you wanna become a singer. Second, you have to learn your body. Larynx, trachea, thorax, deeapragma . . . ' Her hands travelled down over her ample bosom. 'Then you have to have the control, like the car. Because making a high speed in the car, is (Photograph omitted)

the easies' thing. The voice is the same. To make a big soun' this is the easies'. But to control the car, goin' slowly to a bigga speed, with no one noticin'. This is how you have to sing. Den you mus' practise.'

And do they? 'No. No. They don' . . ' Caballe insisted. The interview was rapidly escalating into a performance. And in her zeal, the sweat had turned the talcum powder on her bosom into a high-water mark above her cleavage.

(Photograph omitted)