Of all the writers associated with Rebel Inc, the countercultural Scottish magazine which appeared in the early 1990s and launched the career of Irvine Welsh, Alan Warner has always struck me as the one with by far the most potential. He has the kind of unflinching hyper-realism that shades into the surreal, and has ambitiously avoided becoming typecast: readers of his "chemical generation" debut, Morvern Callar, could hardly have predicted the gothic extravagances of its sort-of sequel, These Demented Lands, nor that after that he would write an acutely observed evocation of schoolgirlhood in non-metropolitan Scotland, The Sopranos. That said, I have, until now, had a degree of scepticism about the extent to which his evident potential has been realised. A novel such as The Worms Can Carry Me To Heaven seemed to me, to use Walter Scott's wonderful phrase about the novels of Tobias Smollett, "sedulously laboured into excellence". Even Morvern Callar seemed to swither: was Morvern's striking amorality, her disavowal of cause and effect, inexplicable or just not explained?

Such caveats no longer apply. Warner's new novel, The Deadman's Pedal, amply fulfils his talent. It is not merely by far his best work to date, it is an exceptionally fine novel by any standards; and although it is wholeheartedly Scottish it would be an immense shame were it to be pigeonholed as a "Scottish novel": its themes  the transition from childhood to adulthood, the vagaries and subtleties of class distinctions, the intangible nature of desire, the dignity and daftness of work  are universal. That they are expressed through the precise, the local and the specific is part of the novel's charm.

Set in 1973 and 1974, the novel's interlocking narratives revolve around the figure of Simon Crimmons. The son of the owner of a local road haulage company, he has decided to leave school at 16, much to his parents' dismay. A misunderstanding in the labour exchange  Simon thinks that "Trainee Traction" might have something to do with working with nurses  means that, almost without choosing to, he becomes a trainee train driver. His father is less than enamoured of his son's choice of occupation. Simon has also just begun sleeping with his girlfriend Nikki, but becomes fascinated with the aristocratic Varie Bultitude, daughter of the "Commander of the Pass". Although both the narrative about the railways and the narrative of Simon's infatuation reach beautifully executed points of crisis, the novel's drama resides in Simon's gradually maturing consciousness, as he learns and mistakes what it means to be a man. Lucozade gives way to lager. A den in the woods begins as a place to play on rope-swings and fantasise about getting a telescope to look into bedroom windows, and becomes the site of Nikki and Simon's surreptitious sexual encounters. It is a novel where even the loss of innocence has a tinge of innocence about it. The central metaphor of the train, involving miles of travel but no change in place, is never overworked.

The Deadman's Pedal is set around "the Port", the fictionalised version of Oban familiar from Warner's previous novels. The demographics of Scotland afford Warner the opportunity to explore class relationships in detail; and the isolated, rural Port is a place where the bampots and the aristos live side by side. As Simon says exasperatedly to Varie in one of the key scenes inter-relating the different aspects of his life, "I've got the whole railway telling me I'm not working class enough and I've got you telling me I'm not middle class enough. This country needs to sort out the class question. As far as it applies to me." There is a cringe-inducing scene where Varie looks out of his bedroom window and says: "Look. Your gardener's working in your grounds." Simon replies quietly: "That'll be my Mum."

Likewise, the heavily unionised railway is both satirised and described with a kind of pre-emptive nostalgia of the present moment. Warner's dialogue is pitch-perfect throughout, with a convincing mixture of camaraderie and carping: when one job applicant "childishly but accurately" points out that all the men swear, and therefore are hypocritical in upbraiding him for it, the union official immediately fires back: "Three times your age, three times the swears, son, so you watch your fucking step talking back to me." The desire to evoke a society as a whole places Warner's new work alongside such books as William McIlvanney's Docherty or Andrew O'Hagan's Our Fathers rather than with the analyses of the déclassé in Welsh or Kelman.

The strain of twisted rural myths, which were such an exciting feature of novels such as The Man Who Walks, is sustained here, and integrated into a form of characterisation. The Bultitudes, whose house is called Broken Moan, have a tradition of being buried in glass coffins, so their remains are visible: this is both a striking image for the aristocracy's necrophiliac possession of the land and something, at least to me, hauntingly familiar (we had similar rumours about the Riddell Mausoleum when I was growing up in the Borders). Both the railworkers and the landowners thrive on anecdote, on tales that reveal the teller.

Warner's language is deliriously vivid. Stars show "uncertain bleats of light"; when Simon has to pee outside, "the transformed beer frothed greenly among the ribs of roots". Although the narrative proceeds in roughly chronological order, there is a very neat switchback, when it jumps ahead and then fills in the details, giving both irony and melancholy to the events. The novel's ending is both bravura and brave: it closes like a diminished seventh chord, an awful pause that could resolve itself into different cadences. The Deadman's Pedal is morally sensitive, exquisitely written and emotionally mature. It could not be mistaken for a book by any other author: Warner has triumphantly come into his own.

 Stuart Kelly's The Book of Lost Books is published by Polygon

There is strange cargo in the coastal waters of the west of Scotland. The North Sea may have its oil; Loch Ness its cryptozoology. But the flotsam sifting into the Atlantic bestows its own kind of marine magic. At Holy Loch, where American submarines spent the cold war salting the water with radioactive isotopes, the story goes that the loch's name memorialises a cargo of shipwrecked Jerusalem earth. And up nearer Oban  the novelist Alan Warner's native soil  the Sound of Mull covers a small flotilla of craft sunk at one time or another by reefs or wartime ordnance.

Warner's seventh novel, The Deadman's Pedal, is punctuated by tales of strange drownings and sinkings. It isn't exactly a new motif: in Morvern Callar  the book that made Warner's reputation  Morvern got high while immersing herself in the night-time Mediterranean. Shipwrecked in its sequel, she washed up on the island shore of what seemed another kind of novel entirely, the experimental and eerie These Demented Lands.

This time we return to The Port, the fictional Scottish town familiar from several of Warner's previous novels. (Across these books, Warner has made The Port an emblematic place, not unlike Hardy's Wessex, or Faulkner's Yoknapatawpha County.) It is 1973. About to turn 16, Simon Crimmons is itching to leave school and to get out from under the control of his overbearing father, the owner of a local haulage firm. Over the course of a summer his life begins to change rapidly as he falls in love, first with a working-class girl from his school and later with Varie Bultitude, the hippyish daughter of a wealthy local landowner. Meanwhile, against the wishes of his aspirational parents, he takes a job on the strike-hit railway as a trainee engine driver. From Simon's railway experience comes the novel's title: the deadman's pedal automatically stops a runaway train should the driver lose consciousness.

Making a rough tally, the submerged contents of this novel include a motorbike, an English ferryman, two soldiers, a weathervane, several coffins, a set of Empire style furniture, some copper saucepans and a whole village sunk to make way for a hydroelectric power scheme. Even dry land isn't: water seeps through the novel, coating the mourners at a railwayman's funeral, darkening torch beams with its droplets, pooling in canvas chairs and rusting cars. The climax of the novel makes neat narrative sense of this pervading dampness but it's tempting more generally to think of Warner as a watery writer, at home on this drenched coastline. His fiction inhabits a shifting littoral zone where accumulated deposits of realist detail  Warner's narrators and focal characters are nothing if not observant  can suddenly shelve off into the deep waters of myth.

At his best in textures, glimpses and sudden twists, he has an impressionist's sense for the way in which the visible and the felt resolves into narrative, though at times in this novel, and particularly at the ends of chapters, he seems to strain for the portentous phrase. One effect of this is the peculiar tic which produces variations such as "these blinded lands", "these evening lands" and "the inner summer lands"  an overworked rhetorical flourish encouraged, presumably, by the book's current of macabre Scots Gothic. And though The Deadman's Pedal abounds in striking images and sharp dialogue, it does seem a little lopsided, as though some major points haven't quite been fleshed out. Indeed, you begin to wonder whether we might glimpse some of these characters again on our next trip to The Port.