Iain Sinclair is a curator of crazed intentions. He found his vocation in his twenties working as a gardener for Hackney Council, cutting the graveyard lawns of Nicholas Hawksmoor's wild churches and, since then, he has only ever looked back. His writing now is an act of vigorous exhumation; he fleshes out extraordinary contemporary satires from an unlikely rubble of old bones. In previous novels - White Chappell, Scarlet Tracings, Downriver - and in his wonderful swirling polemics for the London Review of Books, Sinclair has marked out his territory in the east of the City, Ripper country and beyond, mapping what he likes to call his 'psychogeography' from local poetic myth and buried gangland anecdote.

Landor's Tower is a departure of sorts from this obsessive project in that it sees Sinclair stepping westward on a grudging pilgrimage towards South Wales, where he grew up. The ostensible motive for this journey is a biography of the romantic visionary, Walter Savage Landor. This is a ruse abandoned before it is begun, however, and what begins as a half-hearted research assignment ends, typically, as a diabolic quest for many other things: for fragments of an autobiography, for the secrets and lies of the various utopian communities of the Black Mountains, for the truth of the Jeremy Thorpe scandal, and most of all - Sinclair has never been shy of vaunting literary ambition - for 'a valid poetic for the expiring century'.

This authentic tenor of our times, he believes, lies in 'intentionless narrative: flow, colour, accident', and he does his level best to oblige. Sinclair's fictional method is to hang a discrete series of improvised intellectual riffs on to a Möbius strip of lowlife adventure. A former book dealer, he remains seduced by the double bind of academic arcana and financial chicanery. Within this tonal framework - all of Sinclair's books give off the feeling of having been cast in the back room of an antiquarian bookshop, his prose, at its best, blowing the dust from forgotten treasures - characters come and go.

All, however - including the narrator - are essentially raddled and broken alter-egos: derelicts and shysters with an eye for a rare first edition, paranoid poets with a feel for 'post-contemporary ruins' and filmmakers who look like 'wilted polaroids of what I might become... if I didn't get out of Wales fast...' Like the cartoons of Ralph Steadman, which these caricatures resemble in their wired detail, all lead you inexorably back to the blotted copybooks of their creator.

The Sinclair persona itself is hilarious and unforgiving; in manner, a hybrid of Old Testament prophet and Hunter S Thompson, a gonzo tub-thumper on a road trip into the border lands of the Marches - made to seem here a dissolving line between sanity and madness; genius and gibberish; legend and reality. Along the way this scabrous imagination is trained on anything that might carry hints of pretension: from roll-top baths to stripped pine book shelves; hog roasts to Terry Waite. (Few writers I can think of could summon such righteous savagery for, say, the booksellers of Hay-on-Wye).

Like all would-be prophets Sinclair is drawn to genealogies, not least to prove himself the true keeper of the flame. Here, the invoked tradition takes in a variety of local spirits - Henry Vaughan and David Jones, Eric Gill and Richey Edwards, the missing Manic Street Preacher - a list that runs in tandem with the author's preferred family tree that includes JG Ballard, the extremist crime writer Michael Moorcock and the tribe of poets grouped around the polymathic Cambridge don JH Prynne, from whom Sinclair adopts some of his dense etymological lyricism.

At times, in this literary archaeology, he reaches the outer limits of his curiosity: 'Even with my leathery ego,' his narrative voice jokes, at one tangled juncture, 'I couldn't face the labour of dredging this (Llanthony and Capel-y-ffin) utopian community material for another five years...' It is a relief shared, you have no doubt, by all but his most ardent readers; the sustained erudition of his voice is both wondrous to witness and cumulatively knackering.

It is characteristic of Sinclair to attempt to do the the critic's work for him. He is at it from the outset: 'All of this is so theatrical,' he observes of his opening scene. 'It doesn't have the nervous inevitability of proper fiction. I believe it but I don't care about it. That's the problem...' At one point he claims to aspire to the condition of Barbara Vine and ditch the 'overdressed paragraphs of topography' in favour of a little more whodunit thrust. But the ambition is merely an unfulfilled aside.

Perhaps it is the book dealer in him, but the almost visceral fear in every sentence of this writing seems that of being pulped or remaindered. The result is sometimes desperation prose, each individual phrase clamouring for attention. (For this reason, and for all its commanding intelligence, you never quite lose the sense, which Sinclair would no doubt relish, that the whole book is something a staring-eyed loon might press on you in a subway). At its most extreme - that is, most of the time - Sinclair's singular invention strains for such an outlandish effect. Often this effort achieves its end as baroque comedy. Occasionally - and the surprise is that you do not feel it that often - it comes across as absurd pretension.

Here is the author describing the afternoon scene in his local park: 'Zoophiles gabbed while their beasts were at stool, or sniffing the steaming residue of that operation, or snapping at cyclists; steroidal hoods kicked the shit out of the harmless air; cloud watchers competed for ribbed furniture clear of pigeon droppings...' Such passages are the by-product of a unique, overwhelming stylist.

At one point, in a fragment of memoir, the narrator recalls a boxing bout against the class hard case he had been forced into at his public school. His tactic, he remembers, was to approach his opponent 'from everywhere at once, a berserker...' It is a method he has carried into his writing life. Reading one particularly incendiary section of this book I was reminded of watching a tooled-up video-game hero: Sinclair's prose cartwheeling and somersaulting and jujitsuing through anything the world could throw at it: lobbing smart bombs at soft targets; reducing vain conceits to matchwood, continually taking itself up another level. The effort of staying with this singular writer in this mood can be exhilarating, even if, at times, you feel as if you are not so much reading this novel, as being beaten up by it.