Richard Burton died in August 1984 at the age of 58, shortly before the premiere of Nineteen Eighty-Four, in which he gave his best performance for more than a decade as Orwell's totalitarian apparatchik O'Brien. His diaries cover some 44 years, from his early second world war schooldays in south Wales to the spring of 1983. In May that year he appeared on Broadway in a poorly received production of Coward's Private Lives with his ex-wife Elizabeth Taylor, and on 3 July he married his fourth wife in a Las Vegas hotel. A hefty brick-sized book, it brings to mind the telegram Warner Brothers boss Jack L Warner sent to the director Mervyn LeRoy, who'd inquired whether he'd got around to reading Hervey Allen's blockbuster Anthony Adverse. "Read it?" Warner replied. "I can't even lift it."

The book would have been twice as long had Burton written it with any consistency: there are entries for only a single year (1960) between the schooldays and the post-Cleopatra years of 1965-72, and there are then two further sizable breaks in the 70s and 80s. But with his passion for literature, devotion to education and pride in the brief period spent teaching undergraduates at Oxford, Burton would have felt honoured to be published by Yale and to have had his book edited and annotated in a scholarly manner by Chris Williams, professor of Welsh history at Swansea University and former director of the Richard Burton Centre for the Study of Wales.

At the outset Williams raises the question of why Burton kept the diary and for whom. He suggests, rightly I think, that it was a form of personal and professional discipline, a way of sharpening his prose and his observational skills. As Burton claimed never to reread what he wrote, it doesn't appear to have been kept as an aide-mémoire. But there was money in it (Harry Evans, when editor of the Sunday Times, tells him at a Kissinger dinner party that he'd pay £34,000 for a series of extracts) and the probability of an autobiography. He's insecure about his writing, however, confessing in 1975 that "every word I write I suspect the next day". But five years later, in a relaxed mood while touring in a revival of Camelot, he notes: "I am writing to please myself, though there is a feeling in some place in my head that this may be publishable. I haven't been writing for nothing." It wasn't a secret diary, though, as every entry was read by Elizabeth Taylor, and it was partly kept to express his love for her and to assure her that their life together, however much it resembled The Taming of the Shrew, was secure. From 1965 until their divorce, she makes her own contributions, responding to his entries.

The school diaries have historical interest and great charm as they record, briefly and unpretentiously, a life of poverty uncomplainingly borne as the son of a drunken widowed miner working in a declining mining valley. We read of his love of sport (especially rugby), of books, moviegoing (something he gave up as an adult), playing Monopoly (replaced as a grown-up by a passion for Yahtzee), and attending chapel and taking a critical interest in the sermons. War breaks out; the bombers appear in the skies over south Wales and people die in air raids; a great teacher and student of the theatre, Philip Burton, becomes his guardian, and Richard adopts his name. This is a splendid pre-credit sequence to the big feature that is to be his life. The latter is a sad, sensational story of history repeating itself, first as Shakespearean tragedy on the screen, then as back-stage farce with the fallen hero and his serpent of the Nile playing ostentatious roles before the despised gossip columnists and the contemptible paparazzi, whom Burton calls the "butterflies of the gutter".

The diaries make for a patchy book. They're often tedious in their listing of menus, in the constant rants about how boring children are, and the guilt-ridden, breast-beating accounts of epic drinking and dispiriting hangovers. In 1975 the entries for five consecutive days consist of one word: "Booze". Too many productions go unmentioned, most notably of course the shooting of Cleopatra, to which he later wryly alludes, saying: "All the bad things that have ever happened to me have always happened in Rome." But his devotion to Taylor is passionate and pure, although of the "can't live with her, can't live without her" variety. The jewels, the private jet, the glamorous yacht packed with works by Picasso, Van Gogh et al are tokens of love, as well as trophies of fame. "How posh we are getting," he notes in 1966, but a year later calls himself and Taylor "a lovely, charming, decadent, hopeless couple". At the end her egotism, unreliability and drunkenness during the rehearsals of Private Lives prove too much.

There are occasional well-sustained passages (some vivid pages on a Rothschild ball, a touching little memoir on working at the BBC in the postwar years). The book comes most vividly to life when he's reflecting on specific aspects of the craft of acting, insisting for instance that Olivier, Guinness and Scofield are overly stagey compared with his own naturalism on both stage and screen. And it's at its liveliest when Burton's commenting on his friends, colleagues and acquaintances. He has something to say about everyone, most of it bad, bitchy and pithily expressed. Here are a few random characterisations. Joseph Losey: "arrogant ignorant fool". Franco Zeffirelli: "a ruthless, selfish, multi-faced, ego-mad coward". Warren Beatty: "very selfconscious and actory. He's not out of the top drawer." Olivier: "a shallow little man with a mediocre intelligence but a splendid salesman". Designer Irene Sharaff: "bone-lazy, inflexible, faintly condescending to most people, an intellectual (though she's not overblessed in that department) snob and a crashing bore". Robert Shaw: "Anyone can play Henry VIII: I mean even Robert Shaw has played it." Ken Tynan: "a stammering and stuttering skeletonic death's head. Ken has always looked like Belsen with a suit on. Dachau in Daks. Buchenwald in brown velvet."

Among the few who earn his praise are his mentor and Oxford tutor Nevill Coghill, his Stratford contemporary and fellow Churchill impersonator Robert Hardy, Wolf Mankowitz, Lord David Cecil, and Josip Broz (Tito), whom (at the dictator's personal invitation) he played in the turgid Yugoslav second world war epic The Battle of Sutjeska.

Near the very end Burton quotes a line from Kafka that has haunted him, but "only in the last four or five years has it meant anything to me  I mean only its horrifying and real meaning, personally applied, has it brutally come home to me after all these years in the smugness of the dark." The line from The Great Wall of China and Other Pieces, is: "Only our concept of time makes it possible for us to speak of the Day of Judgment by that name; in reality it is a summary court in perpetual session."

One Sunday evening, in the winter of 1981-82, there was a celebration, at the Duke of York's Theatre in London, of the original radio production of Under Milk Wood. Various participants in that famous broadcast, including Richard Burton, the original narrator, were to read the play under the direction of its producer, Reggie Smith. The theatre was packed, with a largely Welsh audience.

Burton seemed to be enjoying himself, but it was not easy to hear him. He was glued to the book, seemingly in private communion with it. After the interval, the reading resumed. It was evident that Burton had liberally refreshed himself. Now he was not just inaudible but incoherent, with a tendency to slump. The reading lurched to its conclusion, after which the cast repaired to the Garrick Club for a celebratory supper. On the appearance of the first course, soup, Burton gracefully slid into the bowl, face first, at which, it is reported, Elizabeth Taylor (who had made a brief and charming unannounced appearance onstage at the beginning of the evening), briskly pulled his head up, wiped him clean and took him back to the Savoy Hotel.

The wonder is that he pulled himself together sufficiently during the two years which remained to him after this incident to act in a number of films, including his last, 1984, shot the year of the title. Except for occasional brief stints on the wagon, these diaries, at least the vastly longer part of them, from 1965 onwards, could well be titled  as Burton himself suggests, only half-humorously  "The Diary of a Dipsomaniac". His consumption is on a heroic scale. In May 1975, for example, there are six consecutive one-word entries: the word is "booze". On the seventh day, the entry reads: "went into clinic late afternoon". It is the familiar alcoholic pattern: the moroseness, the destructiveness, the self-reproach  what he calls "my mad moods".

By the end of the diaries, neither he nor the reader is any nearer to understanding the origins of his addiction. ("I don't know why I drink so much. I'm not unhappy ") On the face of it, he led a blessed life. Born Richard Jenkins in a Welsh mining village, he left it at the age of two after the death of his mother and thus escaped his father's and his grandfather's desperate lives on the coalface, moving to his sister's house in Port Talbot, where he was lovingly raised. At the age of 16, he met his mentor, the English teacher Philip Burton, one of those extraordinary polymaths who choose to lead their lives in obscurity. Their relationship, which gave the boy a superb education, culminated in the 19-year-old Rich becoming Burton's ward, and taking his name.

From then on, against the background of the war and National Service, he moved from one charmed opportunity to another: after a six-month RAF course at Exeter College, Oxford, and demob in 1947, when he was 22, he was signed up as an actor by the greatest producer of his day, Binkie Beaumont. By 1948, he had enjoyed West End and Broadway successes; the following year he made his first film; in 1951, he had his first classical success at Stratford; in 1952 he went to Hollywood, starring opposite Olivia de Havilland; the next year he had two legendary seasons at the Old Vic, which confirmed him as a great classical actor; soon after he was signed by Twentieth Century Fox. In 1957, at the age of 32, and only 10 years after he started acting, he had to become a tax exile because his earnings were so great; he continued to act on stage, creating the part of Arthur in the successful musical Camelot. In 1962, he met Taylor, their relationship ignited, and together they became for many years the epitome of glamour, immeasurably the starriest acting couple of their time.

And all along, we learn from the diaries, Burton was hating every second of it. The acting, that is, not the life. "I like being famous," he cheerfully admits, and he certainly liked being rich (every so often he stops to tot up just how many millions he has), but he detested acting. "I loathe, loathe, loathe acting  hate it, despise it, despise, for Christ's sake, it." Nothing annoyed him more than being asked by a journalist about "his first love, the stage". He berates one of them for not being able to understand "the indignity and the boredom of having to learn the writings of another man", and the situation in which "you are 43 years old, are fairly widely read", and have to "drag yourself off to work day after day with a long lingering regretful look behind you at the book you're interested in".

He sneeringly dismisses the idea of dedication in actors: "Dedication is an invention of envious journalists. It's all right for your Paul Scofield, or Gielgud, or Larry Olivier, or John Neville to 'dedicate' their lives to the theatre, but, poor sods, no other fucker will allow them on the phone." He prides himself on his professionalism, which amounts to his ability to learn lines, to speak them clearly, to speed the process on. But the idea that there might be something more to acting  that acting might be a creative art  is ludicrous to him.

All this is familiar from the writings of Dirk Bogarde, another actor who saw acting as beneath contempt. Like Bogarde, Burton has ambitions to write; unlike Bogarde, all that he wrote was the diary, and then only fitfully. He can write, no question about it, mostly in the allusive style of the insatiable bibliovore, sometimes with the eye of a sharp reporter: there are vivid glimpses of Marshal Tito (whom he played in a film) and of the playful president of Dahomey; there is witty stuff about his fellow-actors: "Rex Harrison wears clothes as only a coat-hanger can. Clothes, no matter how dreadful, drape themselves around him, knowing that they have come home at last." And there is much intimate material, of course, about the woman he sometimes calls "Glorious", sometimes "One-take", now and then "Fatty", once "Slowtake"  Elizabeth Taylor, whom he palpably adores, despite the booze-induced volatility of their relationship. "I was so fed up, I had three glasses of wine and two large brandies in about ½ an hour, ate my pasta, and went to bed. We shouted at each other a bit but nothing serious." They share an attitude, he thinks, to acting, and to life: "Both Eliz and I agreed solemnly that we never want to work again but simply loll our lives away in a sort of eternal Sunday." And then he adds: "Quite right too. We are both bone-lazy."

The reason Burton  unlike Bogarde, with his novels, his autobiographies, his reviews  never fulfils his dreams of writing is that it would involve sustained work. Similarly his vision of teaching at Oxford  teaching medieval poets in English, French, Italian and German, he fantasises  dwindles into a few personal appearances because it requires hard labour, not least having to learn medieval French, Italian and German. He despises all directors  Huston, Losey, Zeffirelli  and knows that he could do it better than they: of Zeffirelli's dazzling The Taming of the Shrew, he vows, while acting in it, that "never again, if I ever have the chance, will I permit anybody to direct something that I know I am better qualified to do." Somehow, he never quite gets round to it, except once, when he co-directs the disastrous Dr Faustus: halfway through filming, he reports: "I am running out of energy and enthusiasm."

And acting is a dreary burden to him for the same reason: he is "simply uninterested in the work". The key to his understanding of acting is in his remark that "my first love  is not the stage, but a book with lovely words in it." And this is in the end why Burton's acting is so disappointing: even when he's trying  especially when he's trying  he's playing neither a character nor an action; he's simply intoning words, narcissistically resonating them through his superb vocal instrument. This is not acting: it is speaking. And this is why Burton found acting so unsatisfying; he was using so little of himself. He is bored by it. The words bore, boring, bored and boredom appear with monotonous regularity throughout the diaries. Maria Callas is a bore. All children, including his own, bore him "after a while". Like a character out of Lermontov or Chekhov, he gazes at the world with ever-dyspeptic eyes.

But why? Whence all this misery? He asks the same of himself. "I am stupendously disappointed in myself. Something went wrong in my head at the wrong time  I am, I think, sublimely selfish." Well, there you have it, although sublime may not be the word that first comes to mind. Meanwhile, whatever the disappointment, there is a great deal of money to made, and to be spent. It is hard not to turn away from the page in disgust as Burton works himself into a competitive frenzy bidding for a diamond that he eventually secures for $1,100,000. He lightly ironises an earlier, less frenzied purchase, crowing over Onassis's paltry expenditure of less than $100,000 on Jackie Kennedy's engagement ring, whereas he, Burton, gave Taylor a £127,000-ring "just because it was a Tuesday".

He is generous to individuals and to institutions, but when he impulsively buys the private jet he's travelling in (an incident quoted on the cover of the book), it simply turns the stomach. The rewards of the world gratify him, though they, too cannot satisfy him. He is quietly pleased with his CBE, knowing that it may lead to a knighthood. "A couple of seasons at the Old Vic and a stint or two at Oxford and I could swing one fairly easily with Labour in power," he muses. But increasingly the booze obliterates both his life and his career. He and Taylor break up, the relationship having turned into something even worse than the one they so vividly depicted in Who's Afraid of Virginia Woolf?

By the end of the diaries, in 1982, he is appearing in Private Lives, with Taylor, long after their second divorce. There is something infinitely sad about the fact that he now finds her, his Cleopatra, with her apparently infinite variety, finally, "boring" too. The diaries were never intended for publication, and it is difficult to imagine why it was thought advisable to present them at this length. Though the book labours under a critical apparatus that might have been thought de trop if the subject had been Wittgenstein, it is not helpful in telling us about, for example, Taylor's father. The notes, pedantic as they are, are also often simply wrong: Wolf Mankowitz spelt his last name with a W, not a V; the "Trumpet Voluntary" is not by Henry Purcell but Jeremiah Clarke. "God save us all and Oscar Wilde," says Burton, and we are solemnly informed that Oscar Wilde was a poet, dramatist and wit (1854-1900), but not the origin of the phrase or what exactly it means. Burton, a keen and highly critical reader, would have had sharp words to say; words were everything to him. He might have made a splendid Graham Greene-ish foreign correspondent, disgusted with the world, risking his life, propping up the bar, filing his copy seconds before the deadline. He was wasted on acting, and acting was wasted on him.

 Simon Callow's Charles Dickens is published by Harper Press.