Though Andrew Barrow says, towards the end of this eccentric, candid and riotously funny book, that he hasn't thought about his brother Jonathan for years, and that there are friends of the family who don't even know of Jonathan's existence, Animal Magic is a brilliantly mercurial account of Barrow's obsession with his younger brother.

On 5 April 1970, Jonathan died in a car crash on a country road in Buckinghamshire. In the Mini with him was his wild and striking fiancée, Anita. Their wedding was only two weeks away. A double requiem mass was held for Jonathan and Anita on the day that they were due to be married, and in the same church. On clearing Jonathan's desk at the ad agency where he worked, Andrew found an 80-page manuscript called The Queue. In this novel, Andrew discovered to his astonishment that Jonathan had predicted his own death. The page describing the idea of a wedding being replaced by a funeral was still in his typewriter. Forty years later, Barrow takes The Queue and uses it as a highly idiosyncratic maypole around which stories of the brothers' childhood, adolescence and early adulthood cavort and whirl.

Jonathan's novel opens with a man meeting a promiscuous and alcoholic dachshund in a railway station. The dachsund, "Mary", and the narrator embark on a series of escapades, some sexual, some scatological. Mary turns out to be a composite of the family pet Gilda and a dissolute former private tutor and tourist guide called Mr Grant whom Jonathan befriended not long before his death. With its motley cast of schoolmasters, policemen, perverts, dogs and hens, The Queue might at times verge on the prolix or the infantile  it was never completed, let alone edited  but it repeatedly recalls Joe Orton in its macabre preoccupations and scabrous humour. The train on which the narrator travels also carries gorillas, bats and orangutans, many of whom are dead. "Crouching at the controls is a giant rat at least twice the size of a man. Sweat pours from his face and he's obviously in difficulties." If I quote from the novel, it's partly because Barrow has cast his memoir as a gloss or commentary on his brother's work. But there's another, more disconcerting reason. As I turned the pages, I often had the feeling I was reading fiction, and found myself flipping to the back cover to check it really was a memoir.

Had Barrow invented his brother's novel? At times this didn't seem unlikely. The memoir strolls nonchalantly in the twilight territory between fact and fiction. It feels so beautifully concocted. It's just too good to be true.

Andrew clearly sees Jonathan as something of a prodigy, if not actually a genius, and he's not alone among his contemporaries. Even Quentin Crisp, who makes several brief appearances, thinks Jonathan is "extremely odd". "We don't need drugs," Jonathan says at one point. "We're switched on all the time." Jonathan has his own unique take on the world. He reminds us of the extent to which we blind ourselves to the utter absurdity of so-called ordinary life. (One can't help wondering what fun he might have had with Blair's nanny state and its constant bleating about "personal safety".) While under Animal Magic's spell, I constantly noticed signs that might have been lifted from one of Jonathan's notebooks or letters. This, for instance, above a hose-pipe next to a fire extinguisher in an underground garage: "This is not a fire hose". Or this, on a building in the West End: "Alarmed".

As the memoir progresses, however, there is the growing sense that Andrew feels excluded by his brother's eccentricity, and that he would prefer everything to be less amusing and more predictable. Yet he can't relinquish the humour and hilarity because it's precisely that vision that marks the two brothers out from the rest of the world, and binds them inextricably together, for as Barry Humphries reminds the author, the best jokes are often understood by only one other person.

Perhaps I shouldn't have said "inextricably". Increasingly, one wonders about the durability of the bond that links the brothers, and Barrow is brutally honest about the fact that the relationship often feels stalled, or seems to be foundering. He still clings to it, though  or to the idea of it. He can't bring himself to believe that anyone else can appreciate Jonathan the way he does  not the foppish, alcoholic Grant, not the sleazy mover-and-shaker Kenneth Slatter, not even the self-assured and cat-like wife-to-be Anita. Which makes it all the more poignant when Andrew states, matter-of-factly: "Of course I remained excluded from much of his life." There are many such quiet declarations. Barrow has a wonderfully restrained or concealed tone  often tongue-in-cheek, but never arch. His use of anecdote is both masterly and thriftless; he takes episodes around which less skilful writers would have built entire chapters and delivers them in a few perfectly weighted sentences.

At times he comes across like an antic WG Sebald, at other times like a latter-day Flann O'Brien, but in the end he has written a book that is quintessentially  and unashamedly  English. For all its irreverence, this is, in the end, a profoundly moving piece of work, partly because of Barrow's painstaking delineation of the gap that opened up between himself and his "intimate friend", as he calls his brother  a gap that wouldn't necessarily have closed, even if Jonathan had lived  and partly because he has given us such a jewelled description of the years when they were close, conveying just how exhilarating intimacy can be, how fragile, and how precious.

Rupert Thomson's This Party's Got to Stop is published by Granta.

Though Andrew Barrow says, towards the end of this eccentric, candid and riotously funny book, that he hasn't thought about his brother Jonathan for years, and that there are friends of the family who don't even know of Jonathan's existence, Animal Magic is a brilliantly mercurial account of Barrow's obsession with his younger brother.

On 5 April 1970, Jonathan died in a car crash on a country road in Buckinghamshire. In the Mini with him was his wild and striking fiancée, Anita. Their wedding was only two weeks away. A double requiem mass was held for Jonathan and Anita on the day that they were due to be married, and in the same church. On clearing Jonathan's desk at the ad agency where he worked, Andrew found an 80-page manuscript called The Queue. In this novel, Andrew discovered to his astonishment that Jonathan had predicted his own death. The page describing the idea of a wedding being replaced by a funeral was still in his typewriter. Forty years later, Barrow takes The Queue and uses it as a highly idiosyncratic maypole around which stories of the brothers' childhood, adolescence and early adulthood cavort and whirl.

Jonathan's novel opens with a man meeting a promiscuous and alcoholic dachshund in a railway station. The dachsund, "Mary", and the narrator embark on a series of escapades, some sexual, some scatological. Mary turns out to be a composite of the family pet Gilda and a dissolute former private tutor and tourist guide called Mr Grant whom Jonathan befriended not long before his death. With its motley cast of schoolmasters, policemen, perverts, dogs and hens, The Queue might at times verge on the prolix or the infantile  it was never completed, let alone edited  but it repeatedly recalls Joe Orton in its macabre preoccupations and scabrous humour. The train on which the narrator travels also carries gorillas, bats and orangutans, many of whom are dead. "Crouching at the controls is a giant rat at least twice the size of a man. Sweat pours from his face and he's obviously in difficulties." If I quote from the novel, it's partly because Barrow has cast his memoir as a gloss or commentary on his brother's work. But there's another, more disconcerting reason. As I turned the pages, I often had the feeling I was reading fiction, and found myself flipping to the back cover to check it really was a memoir.

Had Barrow invented his brother's novel? At times this didn't seem unlikely. The memoir strolls nonchalantly in the twilight territory between fact and fiction. It feels so beautifully concocted. It's just too good to be true.

Andrew clearly sees Jonathan as something of a prodigy, if not actually a genius, and he's not alone among his contemporaries. Even Quentin Crisp, who makes several brief appearances, thinks Jonathan is "extremely odd". "We don't need drugs," Jonathan says at one point. "We're switched on all the time." Jonathan has his own unique take on the world. He reminds us of the extent to which we blind ourselves to the utter absurdity of so-called ordinary life. (One can't help wondering what fun he might have had with Blair's nanny state and its constant bleating about "personal safety".) While under Animal Magic's spell, I constantly noticed signs that might have been lifted from one of Jonathan's notebooks or letters. This, for instance, above a hose-pipe next to a fire extinguisher in an underground garage: "This is not a fire hose". Or this, on a building in the West End: "Alarmed".

As the memoir progresses, however, there is the growing sense that Andrew feels excluded by his brother's eccentricity, and that he would prefer everything to be less amusing and more predictable. Yet he can't relinquish the humour and hilarity because it's precisely that vision that marks the two brothers out from the rest of the world, and binds them inextricably together, for as Barry Humphries reminds the author, the best jokes are often understood by only one other person.

Perhaps I shouldn't have said "inextricably". Increasingly, one wonders about the durability of the bond that links the brothers, and Barrow is brutally honest about the fact that the relationship often feels stalled, or seems to be foundering. He still clings to it, though  or to the idea of it. He can't bring himself to believe that anyone else can appreciate Jonathan the way he does  not the foppish, alcoholic Grant, not the sleazy mover-and-shaker Kenneth Slatter, not even the self-assured and cat-like wife-to-be Anita. Which makes it all the more poignant when Andrew states, matter-of-factly: "Of course I remained excluded from much of his life." There are many such quiet declarations. Barrow has a wonderfully restrained or concealed tone  often tongue-in-cheek, but never arch. His use of anecdote is both masterly and thriftless; he takes episodes around which less skilful writers would have built entire chapters and delivers them in a few perfectly weighted sentences.

At times he comes across like an antic WG Sebald, at other times like a latter-day Flann O'Brien, but in the end he has written a book that is quintessentially  and unashamedly  English. For all its irreverence, this is, in the end, a profoundly moving piece of work, partly because of Barrow's painstaking delineation of the gap that opened up between himself and his "intimate friend", as he calls his brother  a gap that wouldn't necessarily have closed, even if Jonathan had lived  and partly because he has given us such a jewelled description of the years when they were close, conveying just how exhilarating intimacy can be, how fragile, and how precious.

Rupert Thomson's This Party's Got to Stop is published by Granta.

At the age of 22, Jonathan Barrow, a promising advertising copywriter, was killed in a car crash alongside his fiancee, Anita Fielding. It was a few days before the couple were due to get married. Both of them had been over the alcohol limit, though the police were never able to discern who was driving  something that, according to Jonathan's older brother, Andrew, the author of this unique and touching memoir, troubled their grieving father for several months after the event.

The couple's wedding was due to take place at the Brompton Oratory in London on 23 April 1970. Instead, it became a double requiem with the wedding guests now in the role of mourners. But what made Jonathan's death even more eerie was that he had left behind the manuscript of an unpublished novel, The Queue, in which a wedding turns unexpectedly into a funeral after a bride falls under the wheels of an oncoming bread van. "Tragic, early deaths, even double deaths, are alas not rare," writes Barrow, "but Jonathan's case is stranger than most."

For months afterwards, Barrow touted the manuscript around publishers to no avail. Instead, four decades on, he has written a tribute to his younger sibling that is part-biography, part-elegy, interspersed with extracts from Jonathan's own writing and reproductions of his comic sketches.

The result is a book unlike anything I have ever read. Barrow's reminiscences of his brother's life  from a Wiltshire childhood surrounded by eccentric relatives and a menagerie of animals (including a much-loved family dachshund) to a miserable time at Harrow and then on to a hand-to-mouth existence in late- 60s Chelsea  are touching and heartfelt. But in other places the book is overwhelmed by the anarchic, surrealist tone of Jonathan's own writing.

The Queue, from which Barrow quotes extensively and analyses with painstaking care, is darkly comic, treading a thin line between brilliance and total barminess. The heroine is a dachshund called Mary with human characteristics and a racy past. There are nightmarish visions of screw-on male genitalia, passages about homosexual pigeons and a detailed sequence in which a man is caught having sex with a hen. Beyond this, there seems to be very little narrative. Perhaps the whole thing is a surrealist masterpiece but it is hard not to concur with the opinion of Barrow's acquaintance Quentin Crisp who, after reading the manuscript, said: "Your brother looked healthy, happy, natural But everything else about him is extremely odd. Not faintly odd. Extremely odd."

Barrow writes with obvious tenderness about his lost sibling  the youngest of five brothers  to whom he was very close. Despite, or maybe because of, his idiosyncrasies, Jonathan emerges from these pages as effervescent, clever and hilariously entertaining company but also as someone who did not invite intimacy and who never quite worked out who he was (Jonathan's unresolved sexuality and inner demons are occasionally hinted at but left unexamined).

The text is littered with private jokes which might or might not amuse others. The pop star Mike d'Abo, a Harrow contemporary who went on to become the lead singer of Manfred Mann, is something of a comic talisman for the Barrows who refer to him jokingly in conversations and letters. But d'Abo also makes frequent, inconsequential appearances in Animal Magic so that, in the middle of a paragraph about something else, d'Abo's chart success will suddenly be noted or he will be spotted on the street wearing "purple trousers and red shoes". It all adds to the impression that we are eavesdropping on something that should have remained private.

About two-thirds of the way through, there is a footnote in which Barrow relates that his friend, the comedian Barry Humphries, "reminded me recently that the best jokes are often understood by only one other person". It is hard not to feel that Animal Magic would have been best understood by the one person who, tragically, is no longer around to read it.