It is a brilliant blue winter morning in Oxford. In the city centre, surrounded by golden stone walls and college battlements, the 125th and newest branch of Primark is open for its second day of business. A neat, middle-aged woman comes out of the shop with three full carrier bags. What has she bought? The woman gives a satisfied look. "All sorts. Baby clothes for my grandson ..." She pauses. "Well, handbags mainly, actually." She opens one of her carriers and offers a glimpse of a woven handbag in a pleasing pastel. How many bags has she bought? Her expression sharpens to something between guilt and mischief: "Nine." How much were they? "£3 each." But what is she going to do with nine handbags? Is she going to sell them? "No." She pauses again, as if the answer is quite obvious. "You never know when a bag is going to come in handy when they're £3 a time."

In Britain in recent years, as in other rich countries, many consumer goods have become deliciously, dizzyingly cheap. Since 1995, according to the Office for National Statistics (ONS), the price of women's clothing has fallen by 34%, the price of a vacuum cleaner by 45%, of home audio-visual equipment by 73%, and of personal computers - adjusting the price index to take account of their improved capabilities - by a scarcely believeable 93%. Economists have struggled to find historical precedents for such plunging prices at a time of high consumer demand. "There is a strange conjucture: deflation and boom," wrote the veteran commentator Hamish McRae in the Independent on Sunday in 2004. "There has not been anything quite like this since the 1930s or ... the period 1870-1913," eras when prices fell despite growing consumer appetites.

And in those days there was no Primark or easyJet, no Zara or Ikea, no Book People, Matalan or TK Maxx; no supermarkets or factory outlets; no ubiquitous three-for-two offers; no instant price comparisons via the internet; no weekly women's magazines urging weekly wardrobe revisions; no just-in-time production, and overnight global distribution, and myriad factories humming in China.

"We're in uncharted waters," says Richard Hyman, managing director of the retail analysts Verdict Research. "This deflation is not cyclical. Our forecasts do not anticipate any major increase in retail price inflation ever again."

Hyman, like most adults in most wealthy societies, grew up in the late 20th century decades when inflation was a prominent, recurring anxiety. The public and politicians, and the media, often took rising prices to mean that things, in a cosmic or a very concrete sense, were getting worse. The implications of modern deflation may be equally large. Yet while the production of cheap modern consumer goods, and in particular its social and environmental costs, has justifiably received a lot of attention, the consumption of these products has been examined less. How is the era of the £3 handbag affecting our attitudes to possessions? Are we happier or less content with what we have? Are cheap goods liberating or imprisoning? And what - once we've bought them, and especially once we've finished with them - do we do with them all?

How we shop is the first stage in how we consume, and even a few minutes in the Oxford Primark tells you that shopping has changed. The sound is the first thing: a thick hum of conversation, almost at party volume, anticipation mingling with delight mingling with satisfaction; and the constant plastic clatter of clothes rails and hangers being rapidly rifled. Department stores during the sales sound like this, but not nearly as loud, and the Oxford Primark has opened in February with national consumer activity, according to the official figures, in an even deeper seasonal trough than usual. Yet the shop's plain interior is as busy as Harrods, with people in tracksuits and people in tweed, teenagers, pensioners, mothers and men with fashionable bags. And the Primark shopping baskets they carry are half the size of a beer barrel. In the old days, customers in clothes shops bought things in ones and twos; at Primark, they cater for people buying in dozens.

Many professional observers think this new shopping culture is a great improvement. Hyman says, "There's an American adage: the customer is king. In the UK, all it has ever been is an adage. Now, for the first time, it's reality."

Gareth Coombs of the Cambridge Strategy Centre, a retail consultancy, sees the social implications: "People used to define themselves as shopping at a certain level. 'I'm an M&S shopper.' It defined your place in the world. Those sort of rules aren't sustainable any more." Tamar Kasriel of the Henley Centre, the social forecasters, is blunter: "The idea that cheap goods are for poor people is totally history."

Cheap goods in themselves are hardly new. In fact, it is striking how long the retailers at the centre of the current British bargain boom have been around. Primark began trading in Britain in the early 1970s, TopShop in the early 1960s, and most of the supermarkets soon after the second world war. Resale price maintenance, which restricted by law the ability of shops to discount goods, was abolished in 1964.

Yet, for decades afterwards, more subtle limits on "the value sector", as it was a little dismissively known, endured. Britain being Britain, one of these was class. It is probably not a coincidence that the countries with the longest established cheap retail cultures are the ones with a strong current of social mobility and relative classlessness, such as America and postwar Germany and modern Ireland. In Britain, until the loosening of class structures during the 1980s and 1990s, things were different. "Cheapness had a connotation," says Gillian Cutress, editor of the Official Great British Factory Shop Guide. In 1985, when she started researching her first pioneering book on discount outlets, she quickly became aware that she was entering sensitive territory.

Cutress was an out-of-work zoologist living in Nottingham. She was a Londoner with a determined manner, an interest in factories, and a totally unsqueamish appetite for bargains then considered rare among the professional classes. The East Midlands, she soon discovered, was full of clothing and footwear manufacturers who sold off their seconds and surplus lines at big discounts to staff and people in the know. But these factory outlets were open only a few hours a week and were not advertised: "Many of the manufacturers wanted them to be kept quiet because they didn't want to upset the retailers [which they also supplied]." As Cutress drove round industrial estates asking nosy questions, she also discovered something else: "People made the assumption that our readers would be people with less disposable income."

This assumption proved wrong. "Our readership turned out to be people with time and spare money," says Cutress. Over the next 20 years, her guides got thicker and glossier and came to cover the whole country, selling more than 600,000 copies. More than that, however, they contributed to a slow but significant shift in British consumer thinking.

Until well into the 1990s, the idea that Britain was expensive and that there was little shoppers could do about it was widely held. "Rip-off Britain" became a frequent target for newspaper campaigns, but the solution usually offered was for the government to intervene or for consumers to stock up in the cheaper supermarkets across the channel. Yet while the controversy sputtered on, many shoppers were quietly finding new ways to avoid paying the full price. Factory outlets, like the low-cost airlines that started up in Britain in the mid-1990s, taught people that the price of goods was not written in stone but subject to context and, in particular, the balance of power between seller and buyer. "There is no guilt any more at being brutal about seeking the best price," says Coombs.

Instead of guilt, there is pleasure. As well as the money people save by finding bargains, Coombs and other analysts talk about the satisfaction felt by consumers when they "get a victory" over a retailer - and when they tell their friends about it afterwards. The latter activity, in a sure sign of its popularity, has recently acquired a would-be scientific label: "compulsive price disclosure".

But after you have bragged about your bargains you have to live with them. And at this stage you may become aware that cheap consumer goods do not always go with the grain of other current British social trends. "Over the last 10 years," says Hyman, "we calculate that women have doubled the average number of womenswear items they buy in a year." But over the same period, the cost of living space has been rising as fast, or even faster. One consequence, says David Mitchell, technical director of the Housebuilders' Federation, is that developers are "keeping new houses as small as possible to keep the price down". Meanwhile, planning regulations and the changing tastes of home-owners are filling these dwellings with ever larger and more numerous bathrooms, and more fitted kitchen appliances. The space left over for storage is shrinking accordingly.

"It is a worry," Mitchell says. "Eventually something's got to give between how much we own and how much space we live in."

The solutions may not be elegant. Garden sheds, he says, are growing in popularity, as cheap spaces for general storage rather than tools. "And some developers are making garages half a metre longer than they need to be so people can put stuff at the back." Many homeowners have already gone further: in a current article on outer-London suburbia, the sociologist Paul Barker notes that most garages have been given over to "household junk". The cars are parked in people's front gardens.

For people who have exhausted, or never had such hoarding possibilities, there is the modern self-storage industry. Until the mid-1990s, the idea of keeping many of your possessions in a locked room away from where you lived was largely foreign to Britain, and confined to bigger countries with more mobile populations, such as America. Now there are about 700 British storage facilities, says Rodney Walker, chief executive of the Self-Storage Association, and the business is expanding at 10% a year. "It is a local market in most cases," he says. "Customers live nearby." Does he think the take-off in demand has anything to do with the simultaneous boom in cheap goods? "You're not on the wrong track."

You could see all this hoarding as a sign of a growing attachment to possessions. But Coombs sees it as the opposite. "What was in the living room this year will be in the bedroom next year and in the junk room the year after," he says. Kasriel says the chance to sell to eBay has boosted much we buy. "You can tell yourself you have a sensible financial route out."

Unashamedly "disposable" cheap goods, you could argue, are turning us into traders rather than curators of our possessions. It is another victory for capitalism: we have internalised the unsentimental stock control of the modern retailer. Juliet Schor, an American economist and leading critic of the bargain boom, thinks this new form of ownership is less pleasurable than the old one. "The psychologically satisfying process of personalisation that occurs when products are acquired and retained, is truncated," she writes in a recent essay. "Attachment is briefer and there is the constant pain of divestiture [getting rid of things]." What individual possessions represent to us is, she says, "more externally driven" - by marketing and advertising - and "less under the control of the individual consumer".

Shoppers at Primark in Oxford are cheerier about all this. "I was brought up with thrift," says an elderly man with a cravat and a perfect white moustache. "Brought up not to buy anything unless the old thing was worn out. But three T-shirts for a fiver ..." He holds them up: "They look very good." His eyes sparkle: "This is incredible."

I ask the woman with all the handbags what she does when her cupboards get full at home. "I'll just have a clear-out," she says without hesitation. "Take stuff to charity. Chuck it away if it's broken." Another woman, prosperous-looking, who has bought a duvet, towels and T-shirts for her three children, says with a mildly troubled expression: "I know we live in a throwaway society. It's bad for the environment. It's wasteful. But at home, when we can't fit anything more on the clothes rails, I try and pass it to a collection for the third world." She says her family reaches this point "quite often".

Mending things is coming to seem old- fashioned. "The financial equation's changed," says Coombs. "The price of getting a DVD player looked at is probably half what it cost. And we're time poor. Why waste the time?"

On Tottenham Court Road in central London, the capital's traditional quarter for selling and fixing electronic goods, a man called Vic is living with the consequences of this shift. He has been repairing gadgets round here for 20 years, but his current premises feel less than permanent. At the back of one of the more downmarket shops there is a sign partly obscured by a cheap flat-screen television; through a nearby open hatch, there is a windowless room full of shelves and ailing camcorders where Vic works.

"Ten years ago, people started closing the local repair shops," he explains, with his trademark mix of patience and weariness. "But if anyone brought anything into a shop round here to be fixed, the shop would say, 'Go to Vic.' Now the shops say, 'Don't bother. Just buy a new one.'" He claims manufacturers are deliberately making disposable products: "They only last as long as the guarantee. So they can sell more rubbish. If the machine needs a part, you have to buy it from the manufacturer for £100, £200 - and we have to put labour on top. If I can't charge £50 [for that] I can't survive around here."

He says he can fix so many different gadgets that there will always be work for him. But in future, he believes, electronic handymen won't exist; there will only be specialists, mending the most expensive items. Everything else will be thrown out at the first hint of malfunction.

According to the European Commission, "Electro-scrap is the fastest growing waste stream [in the EU], growing at 3-5% per year", three times faster than domestic waste in general. In 2002, a European directive was issued requiring member countries to ensure the "re-use, recovery and recycling" of discarded electronic goods. Some retail analysts think the directive - especially its sections on the "financial obligations of producers" to be environmentally responsible, and on how "consumers will be able to take [discarded] products back to shops for free" - will have a significant effect on the cheap electronics market. But Britain and several other countries have yet to comply.

The harmful metals and chemicals in many electrical goods, and the difficulty of disposing of them, make the less palatable consequences of increased consumption obvious. The afterlife of discarded budget clothing is more ambiguous. Since 1990, the global trade in secondhand garments has grown tenfold. Clothes are collected in rich countries by charities and commercial traders, shipped to poor countries and sold by local stallholders. In some African countries, more than 80% of people buy secondhand garments, and it is the dominant source of clothing.

"Affordability is the key reason," concluded a report by the charity Oxfam last year, "[but] fashion and consumer preferences also seem to be shifting away from traditional, 'African'-style to more 'western'-style clothing." Oxfam also concluded that secondhand imports were likely to have played a role in the collapse of garment manufacturing in parts of Africa since the 1980s. The trade was tainted as well by "considerable customs fraud", which reduced government revenues across the continent. Yet the report identified considerable benefits too; hundreds of thousands of livelihoods in Africa were supported by washing, repairing, restyling, distributing and selling the clothes.

The charity's real worry is not the ethics of the trade but the quantity and quality of the garments nowadays. "Over the last seven years," says Barney Tallack, Oxfam's deputy trading director, "a greater proportion has been of cheaper quality." A T-shirt that costs £3 new can't be sold for much secondhand at an Oxfam shop in Britain. To make the same profit as before the bargain clothing boom began, the shop needs to receive, sort, clean and sell more garments. "We have to work harder," says Tallack.

At the cavernous Oxfam shop in Dalston, in east London, the most profitable in the country, the clothes rails are like crammed graveyards for discount labels: TopShop, Zara, Hennes, Old Navy, George Essentials. The bright clean colours of many of the clothes have barely faded; the garments look hardly worn. In the storeroom behind the shop there are three booths, each the size of several phoneboxes, piled with bags of clothing."They're usually almost filled to the ceiling," says the manager.

The diminishing returns yielded by discount clothing may also ultimately destroy the global secondhand trade. Such items deteriorate quickly, says Alan Wheeler of the textile recycling association. "People in Africa do not want to wear tatty clothes."

For all the pleasures and popularity and modernity of the bargain boom, a strong sense remains that it is too good to last. Even the Primark shoppers in Oxford share it. I ask the woman with the handbags if she thinks the prices of such things will stay this low for good. "No, I don't," she says. Buying nine handbags suddenly seems less like the confident exercise of a new consumer power and more like the nervy instinct of the old-style bargain hunter: never hesitate when faced with a special offer.

The frivolity of buying a £3 T-shirt can be overstated. For the comfortably off, money saved on cheap basic goods can be spent on luxuries. "Connoisseurship moves to other areas," says the social observer Peter York, such as house alterations and designer labels. "But for everyone else, cheap goods are simply affordable."

For a rich country, Britain has a lot of people who are short of money. One of them was the last person I interviewed outside Primark. She was 21, smartly dressed, and worked for Oxford city council. "I shop in cheap shops," she said. "The council doesn't pay enough and Oxford is an expensive place to live. My council tax is going up. The rent, the travel ..."

Since 1995, according to the ONS, average rail fares have risen 36%, the cost of petrol 63%, and the average council tax by 100%. As many goods have got cheaper, many services - particularly those which cannot, for now at least, be performed from countries with cheaper labour - have got more expensive. The ONS index of the overall cost of services is up by almost half over the past 10 years. Then there are university fees, the pensions crisis, unemployment swelling again, the frightening prices of gas and oil; Coombs characterises these contemporary financial pressures as "a vague rumbling in the background" of the lives of otherwise confident modern consumers. Kasriel provides evidence that the anxiety and the profligacy are sometimes linked: "In one of our focus groups last year, someone said, 'You used to save because you didn't know what was going to happen. Now you spend because you don't know what's going to happen.'"

Ethical and political considerations have yet to check this impulse significantly. Western consumers have known about the Victorian environmental practices, pay rates and working conditions of Asian manufacturing since at least the start of the decade. "Poor people [there] are subsidising the standard of living of consumers in the rich north," as Schor puts it. However, she continues,"The connection between labour conditions and price has not yet been made." Or it has been made by consumers, and then quietly put to the back of their minds. At Primark in Oxford, the shoppers all sounded genuinely concerned when I brought up the cheap labour issue, but they did not linger over the subject.

An even less pleasurable topic never came up at all: that there is a political as well as an economic world order that makes modern discount shopping possible. The overwhelming power of America, the lingering power of Europe and the other traditionally rich parts of the world, and recent economic history all play their part. Schor points out that the bargain boom began shortly after the Asian financial crisis of the late 1990s; in countries such as Indonesia and Thailand, there was suddenly an increased supply of people prepared to work for very low wages.

It is hard to read a newspaper without realising that this balance of power between east and west is altering. In this context, the big questions about how we live with our cheap possessions and whether we really like them and what we do when we've finished with them may ultimately be dwarfed by an even bigger issue. "If other countries come to dominate," Schor says crisply, "We may be the ones producing cheap T-shirts".