The youngest of three brothers who became highly distinctive writers in the early decades of the last century, Llewelyn Powys is today the least read. This is surprising, since in some ways he is now the most resonant. At the present time religion and atheism contend in much the same way they did nearly a century ago when Powys first began to publish on the subject, and now as then his approach to this conflict is refreshingly unorthodox. Like his brothers (there were eleven siblings in total), Llewelyn rejected the Christianity of his father, a Somerset parson whom they all loved and revered. But while John Cowper Powys ended up in a Montaigne-like scepticism and Theodore Powys settled into an earthy acceptance of mystery and mortality, Llewelyn became a passionate opponent of religion – a latter-day Lucretius who railed against otherworldly faith as an illusion that spoilt the joy of life. Unlike our more pedestrian atheists, he also recognised the human value of religion, seeing it as a poetic response to the encounter with death that was his own most formative experience.

In November 1909, at the age of twenty-five, Llewelyn discovered he had consumption:

The shock of discovering myself to be really ill had the strangest effect on me. I became like one drunken with wine. A torrent of words flowed from my mouth. I acted as if death were not the end of every child born into the world, but an event which for some mysterious reason had been reserved for me alone. I felt nothing but pride in finding myself laid by the heels so neatly. I liked to get what sensation I could out of it; and yet, deep in my heart, I refused to realise how grave my sickness was. I liked to talk about dying, but I had no mind to die. I liked to rail against God, but I had no mind that He should hear me … My head had been completely turned, and I chittered at Death like a little grey squirrel who is up a fir tree out of harm’s way.

This passage comes from Powys’s Skin for Skin (1925), an unsparing and yet often lyrical memoir of his encounter with the pulmonary tuberculosis from which he would suffer for the rest of his life. When writing the memoir, Powys mined a diary he kept during his year in a sanatorium at Clavadel near Davos in Switzerland, and it is this journal, meticulously edited and annotated so the reader can catch the significance of its many literary allusions, that the Powys scholar Peter Foss has given us.

With an immediacy the exquisitely written memoir cannot match, the diary reveals how this high-spirited young Edwardian reacted to the onset of a disease that, before the advent of antibiotic treatment, was commonly regarded as a death sentence. Powys lived on for thirty years, dying only in December 1939 as a result of a perforated ulcer. During all of this time he fought ceaselessly against the disease without sacrificing what he regarded as life’s supreme pleasures. For him the sanatorium was not only a place where death was always near, but a sexual playground where the morality in which he had been reared could be shaken off and forgotten.

On Sunday 10 July 1910, Powys suffered a haemorrhage. At this point the diary entries come to a stop with the word BLOOD, which is itself written in blood. When the entries are resumed, over a month later, they record Powys continuing in erotic encounters with fellow patients by whom he risked being reinfected and dallying with a girl he met on one of his no less perilous mountain walks. Amid these interludes and bouts of fever and coughing, Powys fortified himself with readings from Andrew Marvell and Thomas Hardy, Pater and Maupassant, Nietzsche and Wilde. This rich intellectual fare nourished the philosophy that was emerging in him – a starkly uncompromising version of hedonism, which unlike that of Lucretius was willing to risk peace of mind, even life itself, in the pursuit of heightened sensation.

In all of Powys’s writings – the two books of impressions of Africa he wrote after travelling there for his health and spending five years in the bush as a sheep farmer, his accounts of his travels in Palestine, America and the Caribbean, the dozens of short articles and essays celebrating the landscape and life of Dorset, where he later settled, and the ‘imaginary autobiography’ Love and Death, completed a year before he died – he presents life as a gift of chance, which can only be fully appreciated once any belief that it has intrinsic meaning or purpose has been left behind. Accepting that his illness was incurable, he knew that the pursuit of pleasure would never be without pain. As Philip Larkin wrote, Llewelyn Powys is ‘one of the few writers who teach endurance of life as well as its enjoyment’.

In a richly illuminating introduction, Foss situates Powys’s diary in an early 20th-century literature of the tuberculous experience of which Thomas Mann’s The Magic Mountain (1924) is the best-known example. To my mind the vignettes in Powys’s diary are more vividly memorable than Mann’s set pieces: Powys’s fellow patient ‘the philosophic Hungarian’ Dr Szende, author of a book on Napoleon, lying dying in bed reading Schopenhauer while ‘inhaling some white powder and smoking an enormous cigar’; the aftermath of the death of ‘the pachydermatous German’, when ‘four figures tip-toed along the white corridors and down the marble staircase, bearing on their shoulders a long and heavy burden’ to be taken to ‘the Dead house in Davos’; Powys on a twilit balcony shrinking from a lover, a ‘beautiful white-limbed vampire’ with whom he had recklessly frolicked; or talking with his closest friend in the sanatorium, an English ‘scholar and gentleman’ called Wilbraham, whose conventional pieties Powys mercilessly mocked. At times the atmosphere recorded in the diary is so heavily sexualised that Foss comments, ‘One can almost smell the semen on the page.’ At others the mood is one of pathos, as when Powys writes of the girl from Cornwall who yearned for nothing more than the companionship of her dogs.

An unfinished story written in 1912–13 that Foss includes at the end of The Conqueror Worm makes clear the lesson Powys took from his illness. The experience did not make him more prudent or in any conventional sense more moral. Instead it strengthened his resolve to enjoy life ‘without restrictions’. ‘If God restored me’, Powys wrote, ‘I thought I would live more eagerly, more wickedly than ever and with far more craft.’ Recording a bold and original mind seeking and finding delight in life while facing the prospect of imminent death, this must surely be one of the most remarkable diaries that has been published in many years.