"If you don't mind me asking, what exactly do you do for a living?", asks one of the lads.
"Tramps! They're tramps!", snarls the old grouch.
"No, seriously, what are you doing?"
"We're going to walk, and take pictures while we walk, and write about walking."
"They're on drugs! They're all bloody drug addicts!"
"Does that mean that one of you might turn out to be a famous book-writer?"
"He already is," I chip in, pointing to Sinclair and pulling the ocular proof out of my back-pack.
While the angry old man chumbles and sputters and growls away, the likely lads - who explain that they are, in fact, "payroll boys", whatever that means - scrutinise our credentials: three of the four books the Stakhanovite Sinclair has just published or is just about to publish: Crash, his critical study of Cronenberg's film of JG Ballard's novel; Rodinsky's Room, his unexpectedly moving collaboration with the young artist Rachel Lichtenstein about the sad and curious case of David Rodinsky, the vanished East End autodidact and cabbalist; and another collaboration with the photographer Marc Atkins, Liquid City, a sort of delayed companion volume to Sinclair's account of wanderings around London, Lights Out for the Territory. (The fourth new Sinclair book, I later learn, is called Rodinsky's A- Z. Where does he find the time?)
The payroll boys are placated, if not exactly impressed, and one of them launches into a not-many-people-know-that monologue about peculiarities of the region: "Thorpe is the only village in England to have two greens..." "Already I'm fascinated," groans his mate. "...and it also has the biggest green in England. Now, St George's Hill, that's where Cliff Richard lives, a bunch of squatters moved into the mansion that Tom Jones used to live in..." We pay up hastily and beat a retreat for the nearest cash point, while Sinclair footnotes the aborted Tom Jones story with references to the Levellers, who used to occupy St George's Hill three-and-a-half centuries ago.
As we walk at a sprightly pace down into Staines town centre, Sinclair explains what he's up to in slightly more detail. Having devoted much of the last three decades to walking the streets of the East End and the City of London - part self-disciplining pilgrim, part Baudelairean or Benjaminian flaneur, part low-life anthropologist and psychogeographer, Sinclair has now resolved to go further afield, and is gradually making his way around the M25 in an anti-clockwise direction.
He started off from his doorstep in Hackney, went to the Millennium Dome, doubled back on himself and headed north up the zero longitude line as far as Waltham Abbey. He plans to make it back to Greenwich, the meridian and the Dome just in time for the year 2000 beanfeasts. Then he'll go back to key sites with Marc Atkins for photographs and in-depth studies, and the whole odyssey should appear in print circa 2001. Today's stroll, which will probably take us through Staines, Egham Hythe, Thorpe, St Anne's Hill, Chertsey and Weybridge and then back to Staines, is the fifth leg of the M25 orbit.
Tutored in the rudiments of psychogeography by having read and re-read Sinclair's work avidly over the past few years, I can make at least a beginner's stab at reading the superficially unexotic townscape of Staines in the proper spirit. I notice the bust of Mercury above the door of the Post Office (not only are the Old Gods not dead; they don't even bother to hide), a huge poster reading "MADHOUSE UK" (asylums have proved to be the principal staging-posts for the northern part of Sinclair's orbit), the unmistakable evidence that a stonemason has had to correct a lithic typo in the Lawrence Binyon poem engraved on the war memorial, and, of course, the omnipresent security cameras.
Psychogeography, you will have gathered, is an attempt to read a location in terms of its associations. As practised by Sinclair, it's a business of seeking out, inter alia, the hints buried in place-names, or unwitting historical repetitions (Civil War Levellers to Tom Jones squatters), or the traces left by those writers or painters or criminals who have passed this way. In Sinclair's books, these eccentric investigations are liberally spiced with harsh observations about media chancers and halfwits, glum prognostications about the venality and shallowness of our mercantile culture, and plenty of lively, self-mocking knockabout. (I must confess that I lap this stuff up.)
We pass through Staines churchyard, come to the river, potter along the bank and talk incessantly as we go. The logic of today's walk, Sinclair explains, has been taken from a deliciously potty screed, The Kingston Zodiac, written by one Mary Caine; Renchi found a copy in Glastonbury. Any fule kno that hippies and New Agers believe that the landscape around Glastonbury Tor takes the form of a zodiac; you have to be a real connoisseur of the dippy to know that Ms Caine has unearthed a similar configuration around Kingston. Today's route runs mainly down the backbone of the figure she refers to as The Dog, whose nose nestles snugly against the Holloway Asylum. "There, you've got your headline already: Walking the Dog."
We enter the putative Dog's ear somewhere around Egham, get lost three or four times, pass through an industrial estate, which prompts lurid fantasies about James Bond villains lurking inside the bland warehouses, and head south east towards Thorpe. We talk about the ways in which his M25 progress is turning out to be playing into Sinclair's hands. He hadn't known beforehand that Rodinsky was buried near Waltham Cross, where Sinclair first intersected with his circular path. Among the thousands of cryptic documents abandoned in Rodinsky's room in Spitalfields, he reminds me, were copies of the London A-Z marked up with the walks Rodinsky had made, or planned to make, or dreamed of making. "What I'm doing now is based on Rodinsky's A-Z."
We talk about the nearby hinterland of Shepperton, with its reservoirs and film studio, the territory which JG Ballard claimed as his own, and which is the true spiritual home of Crash. We take pictures of our walk and of each other, and of each of us taking pictures of the others, and speculate about the ways in which they may find their way into the projects this will yield for Sinclair and Renchi. We walk and walk and walk: through the eerie, deserted, museum-perfect quaintness of Thorpe, along the nettle- clogged footpath that runs past Thorpe Park and its amusements, and up St Anne's Hill.
By this time almost five hours have passed, and the metaphorical tenderfoot is also a literal tenderfoot. I've chosen the wrong kind of boots, the wrong kind of socks; the soles of my feet are blazing, and by the evening will erupt into a gratifyingly spectacular crop of blisters. Sinclair and Renchi take pity on me, and we stop off at a pub for lunch. Renchi finds a bowl of water for my feet, and Sinclair photographs me as I soak them.
I am painfully aware of the risk that Sinclair may well end up incorporating this undignified spectacle in some book or exhibition, alongside selections of my more ill-considered utterances, but console myself with the thought that there are worse fates than a walk-on, or hobble-on, part in the continuing Sinclair oeuvre. "You'll have learnt to do this sort of thing by telephone next time," Sinclair says, as we head down into Chertsey so that my story can have the aesthetic rounding of a return to the river before I bail out and catch a train back to Waterloo. On the contrary: give me a good pair of socks and boots and I'm up for it again. I've no objection at all to re-branding myself as a pedestrian writer.
`Rodinsky's Room' (Granta Books, pounds 20); `Liquid City (Reaktion Books, pounds 14.95): `Crash' (BFI Publications). `Rodinsky's A-Z' is available from Goldmark Books, Uppingham (01572-821424). An Artangel commission, `Rodinsky's Whitechapel', by Rachel Lichtenstein and Iain Sinclair, will run from 2-30 June, including films, talks and walks. Details from 0171-336 6803 or www.innercity.demon.co.uk/Reuse content