" If you replaced every logo, advert and brand image you see on the high street with a quote from the Bible, you would feel that you were living in an intolerably strict religious state ," I said to the cab driver, as we rode the small hump of a bridge. He didn't brake over the crest, my stomach went giddy. "I mean, if you took all the billboards and put Jesus on them, there'd be a revolution. If you replaced the icons of one ideology with the icons of another, you realize the absurdity you've been living with, everyday, your whole life."

It was an interesting thought, but an idiotic thing to say, when I really should have been giving directions. To his credit, the cabbie was blasé about this riff. He'd just confessed to me how he lost his job during the last recession, and I'd taken it as a cue to sound off on my increasing obsession with consumerism. In turn, he stayed schtumm during my rant while he waited for an equally tenuous cue to bring his ex-wife into the conversation. Unfazed—as ever—by the indifference of my audience, I launched into a description of an artwork I'd devised in the pub: You paste up photographs taken from the darker slumps in 20th century history—say Stalin's gulags—then over them you paste an actual advert. Then, you strategically tear that advert to reveal the real terrors of history that lie beneath the fabrications of the eternal present. "My ex-wife used to be the woman in the shower from the Shield soap advert," he said, tapping his index fingers against the wheel while we idled at the light. "She doesn't look like that anymore, that's for sure."

Adverts are appearing at the bottom of golf holes, above urinals, on the side of eggs, the back of receipts, bus tickets, and on the billboards that are colonising the city. London has become a city of brands. But no-one seems bothered. Except me. You have to fight tooth and nail for planning permission to adjust the roof of your house, but no-one bats an eyelid when a 30-foot billboard is slapped onto a wall. The fly posters go up, no-one takes them down, the corpses of long-dead promotions hang about for years. The demands on your attention are close to unbearable. When, that is, you notice them, when the background flips to foreground, and the procession of provocative adverts rattle around in your consciousness rather than slipping smoothly into the unconscious. "Advertising is the rattling of a stick inside a swill bucket," said Orwell, an attributed quote I have never quite understood. Unless he means the mind is the swill bucket, my mind.

"Ambient advertising"—the business of putting adverts in public spaces—is a booming industry. It has outgrown all other advertsing sectors in the last three years. In 1995, it hauled in profits of £10 million. In 1998, these have grown to about £58m. It has taken the metaphorical advertising phrase of "selling space" literally, snatching up the places where your eye falls, and—in that pervasive new corporate ethos—making them work harder. Why should the side of that house waste its time just holding up the roof when it could also be promoting 'Smints? Adverts are making the bricks shout, the railings wail, and the windows threaten one another with bitter asides—incessant eye noise, and I'm the only one listening to it.

Ridley Road market is off the Kingsland Waste, next to Dalston Junction, in Hackney in East London. But it could easily be in Marrakesh. The market is a cultural pile-up: The sounds of Cypriot, Bangladeshi, Turkish, Nigerian, and cockney compete for your attention as you turn the corner of Dalston Lane. The faded red canvas roofs of the stalls are crammed before you, romanticised by the noon steam of a Saturday. If you walk through the market, you notice how swiftly one culture merges into the next: Gospel music from one stall will be replaced by pig cheeks two paces later, four paces and you can admire the braids of hair for sale, six paces and there'll be someone flogging you cheap lemons, knock-off Teletubbies, a bag of salmon bones. Hands stuffing apples into a paper bag, twisting it shut, presenting it, reaching out to the tomatoes. Hands weighing fish, flinging them onto ice, gutting them. Everything is quite at once and around you and wanting you to buy it.

Walk beyond Ridley Road market, into Dalston Junction, and pick up the 38 bus. It will take you down Balls Pond Road, and soon the murals of Hackney's community art will give way to billboards and fly posters as you speed into the more affluent area of Islington. But the clamour of Ridley Road doesn't ease away. Rather it becomes a visual barrage. The lamposts will be spattered with stickers for singles that have long since left the charts; bus shelters will blare out the latest butter substitute (in Britain, we already have the seminal I Can't Believe It's Not Butter! and the tasty newcomer Utterly Butterly); black cabs will cluster, each one bearing an advert for a fitness centre, the Financial Times, the Yellow Pages. The traditional press of the street market shifts into the brand pulse of modern consumer market. On High Street, cardboard squares will be inserted inbetween the railings running down the centre of the road, advertising a West End Show, or a newspaper exclusive. You might head down to Old Street, where the roundabout is topped by huge billboards advertising financial services, quality products for the affluent citizens driving up from the nearby City, home to London's stock market. Or you might push onto Clerkenwell, the pace of the posters accelerating, each one demanding your attention, giving your experience of the city a stroboscopic feel.

It's all about grabbing your attention, making it pay. Think of attention as a commodity. Others have. In a typically grandiose article in Wired last year, Michael Goldhaber hypothesised an entire attention economy, in which the behaviour he had observed on the Internet (where the attention a site receives creates its value) applies to the real world of jobs and goods. His vision of a society exchanging attention as payment sounds like the fantasy of a commune of narcissists, I know, but his first premise is sound. It is incorrect to speak of an "information economy," because information is an infinite resource, and you can't have economic forces without scarcity. So it is more accurate to place attention at the centre of the information age. After all it is scarce, and its value is easy to measure, determined by the status of owner of the attention.

The attention of a broker controlling investment funds can be worth millions, if you are the company (or country) lucky enough to attract it. The entire Internet is funded on the promise that some day the attention that sites receive will transform itself into money. All of which is by way of saying that you have only so much attention at your disposal each day, and—the same way you can grow to resent the emotional imposition of beggars—I resent having to pay mine out to ambient adverts.

Speaking of which, when I started thinking about all this I couldn't figure out whether the limbs hacked off a child beggar in Delhi were the origins of the attention economy, or its end. Being hacked apart by your parents or your pimp for one second of a rich man's gaze could be a cynical extrapolation of where ambient advertising is leading us, or a telling glimpse into its past. What has changed is the time over which the attention economy functions. Modern advertising can afford to be less immediate than a stump, it can wait until you wander into a shop, maybe months later. Brands are in it for the long haul, beggars—and street markets—are not. They need you to pay up there and then, and that calls for the shock tactics of pity or intimidation.

A ride back from work on the 38 bus, back up from Islington and toward Ridley Road Market. In five second intervals, a billboard ripples from one advert to the next: a battery bearing its muscles, a blue beachscape, something else, I don't know, now I'm looking at a Turkish man strolling down the street with his beaten leather jacket over one shoulder, then a woman with a pushchair out in front of her and a toddler trailing behind. "It's the city, the city, the city," I'm repeating in my mind. Then I'm trying to spend my attention on scraps of the pastoral—to see the sky again, or a scurf of grass washed up on the side of the road. I mean this is only the trip home from work, there is no reason for me to get so worked up. But I'm playing with myself, simulating fast-cut editing by focusing in on the ads and the images, then the people and the planes in the sky. Not so much the eye imitating the camera, as the mind imitating the editing suite.

It's the adverts that start to crank up my sense of claustrophobia. Now that I have begun to notice them, I cannot ignore them, and spot brands everywhere I look. I count out a five-brands-a-second frequency on my walk down my street, picking them off the back of parked cars or toys glimpsed over fences. There is a storm of attention at major junctions. A hurricane of attention on Oxford Street, where most tourists trudge for their Saturday shopping. This attention weather passes over London, and leaves behind heaps of brands that gather in the lee of the streets. Empty wrappers, spent desires.

I confuse this pile of branded junk with the parts of my identity I have slewed off as I have moved through successive consumer cycles. It's a confusion of the junk inside and the junk outside. It could be considered to be a new branch of psychogeography—where instead of studying the effect of architecture, religious symbolism, and history on the character of the citizens, we investigate the intersection of the city, its marketing architecture, and the mind.

London is no longer aloof. Its sheer stone indifference has been covered with promises and imprecations. The clamour for your attention that characterises the traditional market place—like Ridley Road Market—has spread, and each promise is aimed at You, and You alone. A ride around the streets makes you think the whole city is about You, things that You might want, people You might become. London is a narrowing state of consciousness. It's all I can think about. Ask my cabbie.