Swafford says: 'His historical image seems to be that of a plodder, an artist who made himself great by sheer hard work. In fact, he was blindingly gifted . . .' Swafford has clearly warmed to his subject. Although difficult and sometimes downright nasty, Brahms was never boring.

He knew all of Europe's greatest composers and virtuosos, and had fractious relationships with many of them.

Particularly moving was his 40-year friendship with Clara Schumann, which Swafford describes in detail.

There are short sections of the book in which Swafford analyses Brahms' most important compositions where an ability to read music is an asset. But for the most part, this is a biography that can be enjoyed by both musicians and laypeople.

All Brahms' biographers face a difficult task, because he destroyed most of his personal papers, or at least those he thought might incriminate him. He wanted posterity to judge him from an image of his choosing.

He was born in the slums of Hamburg in 1833. His father was a mediocre horn player in a brass band, but he was savvy enough to notice that his eldest son, at age six, had perfect pitch. Young Johannes began composing at age 11.

As with most people, his childhood and adolescent experiences had a profound effect on Brahms the adult, and were largely responsible for making him a very mercurial and distant person. Like all young piano virtuosos, he spent hours alone practising. He was deprived of the early relationships, through play, that help us to learn how to be part of our society. He grew up without any of the necessary social airs and graces. At soirees in Vienna, where the rules of social etiquette were strictly observed, if Brahms 'was not feeling generous things got ugly'.

He was not so much cruel as insensitive, and his tactless comments alienated good friends. Yet he was extremely generous, sending a large portion of his earnings to help his impoverished family in Hamburg.

His relations with the opposite sex were always troubled The roots of this problem went back to his teens, when his father, desperately short of money, put young Brahms to work as a pianist in the Hamburg dockland bars-cum-brothels, known as lokale. For the best part of a year, Johannes played the piano through the night while sailors and prostitutes drank and copulated around him. As a young romantic, steeped in the beautiful music of Beethoven and Mendelssohn, reading Goethe, he was forced to look at the dregs of humanity. These two opposites never synthesised: he never had a fulfilling physical relationship with a woman. The greatest sadness in his life, caused by the lokale trauma, was that he never married but remained a misogynist, visiting brothels when he needed sex.

Those experiences also gave him a ruthless determination to succeed. He realised that genius was wasted without hard work, saying of composition: 'Work at it over and over again . . . Whether it is beautiful is an entirely different matter, but perfect it must be.' As Brahms' genius developed he outstripped his teachers, and in September 1853, while on a holiday touring the Rhine, he went to Dusseldorf and finally whipped up the courage to knock on Robert Schumann's front door. As he was invited to play one of his works, Schumann called his wife Clara into the drawing room and declared: 'Here, dear Clara, you shall hear music such as you have never heard before.' Here was the perfect couple converted to his cause - Robert, the brilliant composer, and Clara, the finest pianist of her generation. But behind the facade were dark secrets that would not stay secret for long, for Robert was insane. After a failed attempt at suicide, he spent the last two years of his life in an asylum. Brahms had fallen hopelessly in love with Clara, the first of the women he would put on a pedestal, worship and then spurn. She was 34, he was 22.

After Robert's death, she responded positively to his advances, but by then he had changed his mind. Whenever he was on the brink of marriage he got cold feet and retreated to the lonely world of his bachelor rooms. When she died in 1896, Brahms wrote: 'Apart from Frau Schumann, I'm not attached to anybody with my whole soul . . . Is that not a lonely life!' He could certainly never be accused of indecent haste. His First Symphony took him 12 years to complete. But once he had crossed that orchestral Rubicon there was no stopping him. Between 1876 and 1878 he wrote his first two symphonies and his Violin Concerto. He then produced a major orchestral work every second year until 1887 - 'each of them', says Swafford, 'an unquestioned masterpiece'.

He was to spend most of his adult life in Vienna, at that time the musical centre of Europe and, therefore, the world. It was to witness his greatest musical triumphs.

He had by then joined the respectable ranks of the middle class and it was for them he composed. Many of his admirers were accomplished amateur musicians.

They belonged to a city and to an empire which was in decline; they adhered to a philosophy, politically and musically, that was to be overtaken by events. Brahms waged a relentless war against a musical movement known as the New German School. Led by Wagner and Liszt, this group believed that the arts should be united; that music could not exist in isolation.

Brahms found his musical voice at a relatively early age and it never changed.

By schooling himself in the works of earlier masters, he was able to combine different styles in a way no composer had done before or since.

As one contemporary musical critic put it: 'He understands how to be Classic and Romantic, ideal and real, and, after all, I believe he is appointed to blend both these eternal oppositions in art.' In the 20th century, modernism and expressionism seemed to be the antithesis of all that Brahms had stood for. But there is no substitute for craftsmanship, and the techniques he employed that made him such a consummate musician were not forgotten.

In 1947, Arnold Schoenberg, modernist par excellence, wrote an article in which he said that Brahms had united 'the once separate domains of melody, harmony and form'. This, he added, was 'one of the seminal developments in all music'.