After London, or Wild England (1885) is a novel with evident flaws. Even its admirers, who include several literary heavy weights such as John Fowles, acknowledge this: 'Nothing, beyond blindness, can make of Jefferies a nature-writer of less than genius; and nothing, beyond an excess of sympathy, can make him a great novelist' (Introduction, xiii). As Fowles suggests, echoing the general consent, Jefferies is a nature writer par excellence – his impressive oeuvre attests to this – but as a novelist he has weaknesses that have limited his reputation in that field. In After London, his last book, published two years before his early death at the age of 39, these fault-lines split the book apart.

Essentially a Romantic quest in the vein of the Medieval fantasy popular in late Victorian England (eg The Wood Beyond the World & The Well at the World's End by William Morris) After London stands out as an early example of "post-apocalyptic fiction": after some sudden and unspecified catastrophe has depopulated England, the country reverts to nature, and the few survivors to a quasi-medieval way of life.

Echoing its double-barrelled title, the novel is divided into two halves: Part 1, The Relapse into Barbarism; and Part 2, Wild England. The first half is entirely exposition, convincing but tensionless. Jefferies charts the downfall of civilisation and the return of the wild in loving detail. His nature writing shines forth, but in terms of fiction, it is flat. There is no narrative traction, no dramatisation, and no tension – everything has happened in the past. Jefferies breaks the golden rule of 'Show, don't tell', clunkily filling in the backstory in a ponderous way, terminally postponing the start of the story in the dramatic present until Part 2.

Yet the picture he paints of a world reclaimed by nature is an alluring one – unlike so many post-apocalyptic scenarios which depict a Mad Max-dystopia, nature has healed itself. This is refreshingly positive, bucking the trend of the doom and gloom brigade, even though a vision of a flooded England, as imagined by a Victorian nature writer, is not only incredible prescient but also increasingly likely. The floods of Summer 2007 gave Britain a taste of things to come, as Climate Change causes more and more extreme weather events, and the melting ice caps increase sea levels, encroaching upon already beleagured coastlines. Not only does Jefferies' novel prophesy Climate Change, but also the undeniable prospect of Peak Oil: the point at which cheap oil reserves start running out. Population has dwindled to sustainable levels and humanity returned to a Medieval technology level. Victorian polymath and Medievalist William Morris commented upon it: 'absurd hopes curled round my heart as I read it.'

The second part, "Wild England", is largely a straightforward adventure set many years later in this wild landscape and society (here too Jefferies was setting an example for the genre); but the opening section, despite some improbabilities, has been much admired for its rigour and compelling narrative. Critics dissatisfied with the second part make an exception of chapters 22-24, which go beyond recreation of a medieval world to give a disturbing and surreal description of a fallen city.

Our protagonist, Felix Aquila, is a rather fey and ineffectual hero, perhaps an inadvertent self-portrait of the author, who was always hampered by a poor constitution and wrote the book while suffering from TB, which perhaps gives the later sections their feverish hallucinatory quality. The story creakingly comes alive – told in a rather old-fashioned style even for Victorian fiction (Jefferies follows in the footsteps of Morris, who wrote fiction in a Medieval style). The line of desire is established – Felix wishes for the hand of the fair Aurora and sets out on a quest to prove himself worthy of her. Simple enough – a Fairy Tale dramatic arc – but things do not go to plan. A series of episodes illustrate Jefferies' clearly pessimistic view of humanity, culminating in his tour-de-force: a vision of a devastated London.

Here the novel leaps to a visionary level – and it is this section which redeems all the flaws of the novel. Reading it after the close of the Twentieth Century, Jefferies' vision of an obliterated London seems eerily like the descriptions of Hiroshima and Nagasaki: the shells of buildings, the traces of skeletons sketched out in the blackened earth, the air filled with yellow vapours and spectral fires, the water rank with decay, nature corrupted beyond repair. It makes for disturbing if compelling reading. Coming after chapters of rich, loving description of a Wild England, the London sequence is a shock to the senses: a dark footnote to the natural history of the world – the aberration of civilisation. Its Ozymandian intentions are clear: 'Look on my works, ye mighty, and despair.'

Jefferies interest in catastrophes predates After London: two short unpublished pieces from the 1870s describe social collapse after London is paralysed by freak winter conditions ('The Great Snow'). In the better achieved of these, the narrator is a future historian piecing the story together from surviving accounts. The fantasy of the second part also has a predecessor in a short work, The Rise of Maximin, Emperor of the Occident, serialised in The New Monthly Magazine in 1876, in this case an adventure set in a remote and imaginary past.

Although the society that Jefferies depicts after the fall of London is an unpleasant one, with oppressive petty tyrants at war with each other, and insecurity and injustice for the poor, it still served as an inspiration for William Morris's utopian News from Nowhere (1890).

Felix escapes from this nightmare with treasure, but it is the journey home that proves the most perilous. In this respect, After London follows the classic Hero's Journey pattern as first discerned by mythographer Joseph Campbell (which he termed 'monomyth' in The Hero with a Thousand Faces) and then adapted for screenwriting by Christopher Vogler (in The Writer's Journey). After his Ordeal in the Inmost Cave, where he Seizes the Sword, Felix must survive the Road Back, if he is to Return with the Elixir, in this case, the riches from the poisoned city.

The infamously inconclusive ending is perhaps frustrating for some, as though Jefferies had given up or run out of time (or indeed vitality), but actually it presages the existential novels of the early Twentieth Century, and is powerfully modern in its 'unknowing'. It is an open ending that lets the reader decide the hero's fate, depending upon their own attitude to life.

A few decades later, JG Ballard was to echo it in his ending of The Drowned World (1962) when the protagonist, Kerans, walks into an equatorial jungle. It is the Cloud of Unknowing of the Medieval mystics, the Negative Capability of Romantic poet John Keats, and the No-mind of the Buddhists – a place of rational surrender which sits uncomfortably in the Western mind.

John Fowles summed it up as 'the strangest book that Richard Jefferies ever wrote, if not the strangest from any considerable writer of his period.' It stands out because of its visionary boldness – as with HG Well's The Time Machine, Jeffries is not afraid to take the long view; and as with Well's predictions (aerial warfare, space travel, the atom bomb) Jefferies is uncannily prescient.

Two years later Jefferies was to cross the threshold into the Great Unknown of death, taken before his time by tuberculosis. After London remains a haunting and prophetic vision of the dark century that followed and a future equally as ominous. It is a truly neglected classic, but perhaps one whose time has finally come.