The only time you want to eat chips is when you're really hungry. Or when you're quite hungry. Or when somebody else is eating chips in the same room. When somebody is eating chips close to you, you make a quick calculation. How well do you know that person? Will that person be offended if you ask them for a chip? Will they be offended if you ask them for another chip? Chips, being discrete units of food, rather than a single blob or lump of food, have a social element. They suggest sharing. But still, you often see chips being guarded - plates or takeaway punnets being clutched close to the chip-eater's body, out of striking range; hands being slapped across the table. You often hear the phrase, 'Get off my chips!'

We love stuffing chips into our faces. They are dry enough to pick up and soft enough to cram by the fistful into your mouth. They contain enough grease to slip down your gullet unaccompanied. Every year, as a nation, we stuff more of them into our faces than we did the year before. Chip consumption is growing in Britain by one per cent annually. This may not sound like much, but it amounts to thousands of tonnes of potatoes - preferably potatoes with a medium or high starch content, such as Maris Pipers or Pentland Dells or Idaho Russets. They are stored in vast warehouses, under strict temperature, light and humidity conditions, during which time some of the starch in the potatoes turns to sugar. This is why, when you fry them, they turn a lovely golden brown colour. And this is one of the most desirable food colours on the planet. Golden brown foods can inspire a kind of lust. Get off my chips!

When you eat chips, you feel good. This is because the carbohydrate in chips causes a rapid rise in blood glucose; chips give you a starch high. According to the nutritionist Michel Montignac, chips are a 'bad carbohydrate'. With a 'glycaemic index' of 95, almost nothing raises your blood sugar so fast. This is partly why they are so delicious. Chips are also a nutritionist's nightmare. They can be addictive. Chips are starch covered all over with fat; they are like bread which has been buttered on both sides, and around the crusts as well. Chips are starchy tubers which, typically, have been fried twice; they are potatoes from which the water has been forced out. This is why they are fluffy on the inside and crisp, or even crunchy, on the outside. They are, in a way, a culinary miracle. You just can't do this with pasta or rice. If the West has problems with obesity and diabetes, it is because of foods like chips. This is something we've got to admit. Chips might be one of the best inventions on the planet, but they might also be killing us. When you eat chips, the graph describing the level of your blood sugar resembles a Swiss Alp; you get high, and then you crash. So you want more chips. You enter the chip cycle. Like cigarettes or cocaine, chips are delicious, not in spite of the fact that they are bad for you, but precisely because they are bad for you. They are, perhaps, the ultimate in decadent food. As a cultural item, they are the best and the worst of us.

So what if they're killing you? Sometimes you just want chips. For one thing, chips remind you of being a child, when you burned up so many calories it didn't matter. I spoke to a man who had masterminded several advertising campaigns for McCain oven chips and Microchips - chips which have been pre-cooked and whose packet-to-mouth time is three minutes. Understandably, the man didn't want to be named; he knew there was a chance I might say something bad about chips. Chips are, in a way, a controversial product. But he needn't have worried - saying something bad about chips is like saying something bad about slim, leggy models in women's magazines. It won't make a blind bit of difference. People know what they like.

We were sitting in a slick, bright conference room. The man told me about the campaigns he had participated in. As he talked, I imagined his face pixillated to anonymity. The ads were brilliant and daring. In one, a young girl, stultified with chip-lust, asks herself the question, 'Daddy or chips?' Which would she choose? Which would you choose? In another one, a couple are depicted on a sofa, stealing chips from each other's plates. In a third, black dudes force handfuls of chips into their mouths. That's more or less it - black dudes gorging on chips. It's brilliant. In a fourth, a man resembling David Ginola is, somehow, forced to choose between a chip and a gorgeous babe. It's more profound than you think - if you eat chips like some of the people in the ads, you might find yourself forgoing the pleasures of gorgeous babes.

The advertising executive told me that, according to research, chips are the biggest cause of arguments in restaurants. Couples in restaurants argue more about stolen chips than about their partner ogling members of the opposite sex. 'The thing about chips,' said the man, 'is they taste better if they're not yours. You have to nick a chip off someone's plate'.

People, said the man, want chips to taste fried. Even so, they do not, on the whole, want to fry them themselves. For most chip-eaters, chips must be something fried for you by someone else. Chips, it seems to me, are the ultimate leisure food. Chips are food as play. Chips are, in a way, a sort of holiday. And, like a holidaymaker, a chip-eater wants to engage his baser qualities - laziness as well as greed. This might be why the oven chip is gaining ground over the home-fried chip. Out of every 100 chips eaten in the home, 74 are cooked in the oven, and six come out of the microwave. As a result, the incidence of chip-pan fires is dropping. McCain's Home Fries, said the man, taste like chips which have been fried at home. They taste like they have emerged from a sexy fryer, rather than a much more prosaic oven. 'That sounds like bollocks,' said the man, 'but it's true.'

Imagine yourself holding a chip. You don't hold them for very long, do you? But if you hold a chip which you have not prepared yourself, do you ever wonder where it came from? Probably not. How much time do cocaine addicts really spend gazing down at their next white line wondering about its provenance? But wait. That chip you are about to thrust into your mouth has been on a long journey. Chances are it has been processed by McCain, the world's largest producer of chipped potatoes.

One in three of chips everywhere has been through a McCain factory. If you eat a McDonald's French fry, McCain employees, or contractors, have grown it, harvested it, trucked it, mechanically peeled it, skinned it, trimmed it, brushed it, blanched it, dried it, fried it, de-fatted it, cooled it, frozen it, bagged it, boxed it, X-rayed the box for foreign bodies such as coins or pens, and trucked it to one of three distribution plants in Manchester, Basingstoke, and Hemel Hempstead, from where it is trucked again to the parking lot behind the golden arches in your home town, to be re-fried by youngsters in cheerful aprons.

The McCain head office, and one of three McCain chipping plants, juts out of the desolate North Yorkshire landscape, five miles south of Scarborough. It is a vast, Satanic building, like a huge aircraft hangar bedecked with turrets and chimneys. It steams. This is chip central. On an average day, 1,200 tonnes of potatoes arrive at one end of the factory, and chips - a mind-boggling amount of chips - emerges, packed and boxed, at the other. Paul Major, a cheerful man with his hair cut en brosse, is the factory's production manager, and he loves producing chips. He gets tremendous job satisfaction out of a good day's work, with good line rates and no 'quality issues' with the potatoes. Potatoes are checked and re-checked. They must conform to very strict parameters. 'You just get a buzz out of everything,' Major tells me.

Ernie Thompson, a chip man of 24 years' standing, is in charge of the liaison between McCain and McDonald's. He eats a lot of chips. 'What's the hardest thing about the job? Keeping your weight down,' he tells me. But Ernie is lucky. He is tall and slim, with grey hair and a neat grey moustache. He exercises a great deal. Donning a hairnet, a white coat, and a protective hard hat, items which I must also wear, Thompson takes me into the factory.

It's extraordinary. I've never seen so many potatoes. I am in a vast, cold, soil-smelling space. On one side of me is 100 tonnes of potatoes. Underneath me is a river of potatoes. They have all been grown from sixth-generation seed potatoes which have themselves been transported from their nursery fields, in the north of Scotland, to farms around Britain. Standing on a metal walkway, I follow the potatoes' progress through the factory. They flow into rotating tanks where the skins are blasted off with steam. Then they are fired through 'hydro-guns', forced under high-pressure water through metal pipes. At the end of each pipe is a grid of blades. This is the point where one potato becomes 10 or more chips. To make a McDonald's fry, you arrange the blades so that they are closer together. To make a chunky Home Fry, you place the blades further apart.

And then what? The river of potatoes becomes a waterfall of chips, a Niagara of what chip insiders call 'strips'. It is awesome. The strips are whizzed along on a holed conveyor, to ensure that small ones fall through, into the vast nether world below, the Hades of failed chips, chips that didn't make the grade. Making the grade, explains Thompson, is the crucial thing. Consistency is everything.

Chip eaters want the chips they eat today to be exactly the same as the chips they ate yesterday and the chips they will eat tomorrow. The chips flow past mounted cameras, which photograph any blemishes which might remain; in an awesome feat of technology, blades are programmed to pop up and slice off the blemishes. When you're standing on a thin metal walkway at the top of a cavernous factory building, skidding on fat deposits, and looking down into a swimming pool of boiling fat, you understand what people put themselves through to arrive at the perfect chip. You have plugs in your ears to protect you from the noise of the chip-making process. 'It's a very complex job,' says Thompson. 'People think that making frozen chips is the easiest thing in the world. But it's not.' Later, the chips are tasted by a panel, some of whom are thin, and some of whom are not. In its way, eating chips, like everything else in life, is a lottery.

Major and Thompson, and Graham Finn, McCain's Potato Procurement Manager, are philosophical about their work. They are potato men through and through. Finn, a teacherly man of 51, tells me that McCain's Russet Burbank potatoes are all, every one of them, the descendants of just five seed potatoes brought over from America in the Eighties; now tens of thousands of tonnes are processed every year. 'It's a key part of the role,' says Major, 'getting the right potatoes. If there's one thing I've learnt, it's about getting the right potatoes.' Thompson says, 'you can't make a silk purse out of a sow's ear.'

Look at that chip you're holding. Is it golden? Is it the same as the chip you ate yesterday? Yes, it is. Now you want another. Chip eaters start off by picking their chips out singly; soon, they are picking up bundles of two or three. Sometimes, we eat them out of cones wrapped in newspaper. They have tabloid associations. In a recent episode of Footballers' Wives, one of the footballers says, of the royally tarty model Chardonnay, 'the first time I saw her she was naked, wrapped around my chips'. Chips are wonderfully grungy; this is always part of their attraction.

But it's because of this grunginess, this accepted fact that chips are a part of lowlife, that they can be served, with a touch of irony, in the poshest places. John Torode, who is the chef at Smiths of Smithfield, talks about chips in lyrical tones. 'They are essentials,' he says. 'Absolute essentials.' He is a good-looking, cheeky Australian in early middle age. One of the pleasures of chips, he says, is dipping them into things; chips are excellent carriers of sauces and gravies. The Belgians, who claim to have invented the chip, eat them with mayonnaise. Germans eat them with mustard. We favour tomato ketchup, along with the Americans. 'Just dipping a chip into the yolk of an egg,' says Torode dreamily.

In the hyped world of the celebrity chef, chips are a reminder of earthy pleasures. Gordon Ramsay told me, 'I love a bowl of chips. With rock salt and vinegar. Chefs really love chips because you're surrounded by fancy food all day'. Ramsay cuts his chips thick, in the Pont Neuf style developed in Parisian restaurants; they're about the size of a big man's little finger. Torode does the same; he serves chips, cut from large Maris Piper potatoes, along with £28 steaks in his most expensive restaurant in Smithfield.

Torode takes me into the restaurant's kitchen, where he introduces me to Ashley, a commis chef who cuts his chips. Ashley picks up a large Maris Piper, about the size of a pint glass, and places it on the slab. After six quick moves with the knife, he is left with a brick of potato, just a little bit bigger than a half-pound pat of butter. Three more cuts - the whole thing is over in a few seconds - and Ashley has six near-identical Pont Neuf chips.

'You fry them twice', says Torode. 'Once, for four or five minutes, at 120 degrees, and then, later, for three minutes at 190 degrees.' This is the essential fact about the chip - it must be fried twice. Once to force the moisture out of the chip and seal the outside, and again to make the outside tough and the inside smooth and fluffy.

I am sitting at my table in Torode's restaurant, waiting for my chips. I am thinking about chips. I am chip-fixated. I am thinking of the voice of Ian McCaskill, in a chip ad, saying, 'You just can't help yourself'. I am thinking of people stealing chips from each other's plates, of the Western world getting fatter, of the advertising executive who told me that, in focus groups, some chip-lovers went into what he described as a 'hypnotic chip world'. I am thinking of the chip-loving Cameron Diaz, who once described herself as 'a salty, greasy girl'. The chips arrive. I want the chips! I want to stuff them into my face, like the black dudes in the ad! I reach out, grab a chip, stuff it in. I look around the table and move the bowl protectively towards me. A hand is moving towards my bowl. 'Oy!' I say, 'get off my chips!'

The chipping news

· Chips were first popularised in France, hence the name French fries

· Selling fish and chips was once licensed under the Offensive Trades Act because of the smell produced. During the war it was the only take-away food not to be rationed

· Today there are only 8,500 fish and chip shops compared with 30,000 in 1950

· Britain eats 22,000 tonnes of chips a week

· 44 per cent of British households still use a traditional chip pan, while 34 per cent prefer a deep-fat fryer

· Northerners are most likely to fry their chips at home, with 28 per cent claiming to cook them from fresh every week. Sixty-one per cent of Southerners say they never cook chips from scratch

· In 2000 over 277 million fish and chip shop meals were sold throughout the UK, and in a new UK survey 41 per cent voted cod and chips their favourite takeaway making it the nation's top hot takeaway

· One in four of all British potatoes consumed in Britain are eaten as chips.

· The British Nutrition Foundation found that an average portion of fish and chips contains 20.6 per cent of fat - almost three times less fat than a chicken tikka masala and pilau rice, which has 59.9g of fat

· In the Eighties the industry took the decision not to wrap chips in newspaper because of a suggested link between black printing ink and cancer

· McCain are king of the frozen chip industry, claiming the UK's top three favourite products. First Home Fries, then McCain Oven Chips, followed by McCain Micro Chips

· National Chip Week runs from 11-17 February.

Research by Chloe Diski