Britain is facing a crisis of nutrition. Evidence published in the Guardian this week suggests rising food prices and falling incomes are reducing our intake of fresh fruit and vegetables and increasing our consumption of processed foods: out with oranges and lettuce, in with instant noodles, coated chicken, tinned pies and pizza, with predictable consequences of ill health and obesity. Those most affected are the poor, though "food poverty" affects families that are far from Britain's poorest. The Guardian interviewed a Bristol couple with two young children and a household income averaging £24,500 a year: the wife found it "a constant struggle just to buy enough food to fill our stomachs".

That surprised me. With what were they filling their stomachs? Surely not a saintly menu of baked potatoes, pasta, tomato sauce, tap water, minced beef and the less-than-perfect-looking fruit that supermarkets have finally, sensibly, decided to sell; surely something devilish – fizzy drinks, biscuits, those tinned steak pies that surprisingly are still manufactured. The government, after all, has devised a strategy called the Eatwell Plate, which shows how a healthy, well-balanced diet, rich in fruit and veg, can be achieved for £16.70 per stomach per week. Feeding a family of four at this standard – generously counting a seven-month-old baby as an adult – would cost about £3,500 a year, or 14% of this Bristol household's income. That is a bigger proportion than the average household spends on food – 11.2% of its budget – but smaller than the 16.8% spent by the poorest fifth of households, which roughly equate to those below the poverty line. By official estimates, therefore, the Bristol family don't need to struggle to fill their stomachs – and with nourishing food. They just need to be wiser.

This is an old trope: the British poor need to be taught how to eat better than they do. Cheap Victorian cookery books published recipes advertised as wholesome and stunningly economical – a dinner for tuppence – and sometimes ransacked foreign cuisines to provide something interesting and new. Bouillabaisse, for example: the dietician Sir Henry Thompson thought the poor would lap it up, forgetting (as the social historian John Burnett reminds us) that what was cheap and easily available in Marseilles wasn't necessarily so in Manchester, where a housewife might never find a mullet, a capsicum or a bay leaf, and her husband would find the result disgusting even if she did.

One of the most famous lists in literature occurs in The Road to Wigan Pier, when George Orwell asks an unemployed miner and his wife to write down what they spend in a typical week. They have two children, aged two and 10 months. From a state benefit of 32 shillings (£1.60), half goes on food. Orwell notes that they spend twice as much on sugar as on green vegetables, and nothing on fruit. The basis of their "appalling" diet is white bread and margarine, corned beef, sugared tea and potatoes. Healthier ways of eating for the same money are certainly possible, writes Orwell, reproducing the diet of a letter-writer to the New Statesman, who claims that for four shillings (20p) a week he has a diet that includes three whole-meal loaves, 10 oranges and two pounds of dates. But in Orwell's phrase, the "peculiar evil" of poverty, when it comes to diet, is that the less money you have, the less inclined you are to spend it on "good wholesome food". You want something "tasty" – ice cream, a hot bag of vinegary chips, a nice cup of tea.

That age had its dietary missionaries, too. Orwell quotes an angry Communist making a speech that berates the "society dames [who] have the cheek to walk into East End houses and give shopping lessons to the wives of the unemployed". It was typical of the English governing class, according to the Communist: "First you condemn a family to live on 30 shillings a week, and then you have the damned impertinence to tell them how to spend their money." Orwell says he heartily agrees, and then confuses the issue: "Yet all the same it is a pity that, merely for the lack of a proper tradition, people should pour muck like tinned milk down their throats … " So he's torn. Boo to the English industrial working class for being "exceptionally ignorant" about food, for their hatred of brown bread, their love of tinned peas, their almost automatic rejection of good cooking. But boo also to the Lady Bountifuls who want to rectify things.

Can there be a clearer case of a man having his tinned pie, his coated chicken, his deep-fried pizza and eating it? But perhaps many of us – that is, many of us who aren't poor – have felt similarly divided. Thirty years ago, following Orwell's footsteps around Wigan, I found a similar family to the one who had itemised their budget for him in 1936: unemployed husband, housewife, two young children. Their benefits came to £73.60, out of which a quarter was spent on food. In 1936 this had been easy to break down item by item – bacon, dripping, jam, etc – but by 1982 food processing had provided a wide variety of foodstuffs, bought in such small quantities ("two jars salmon paste, one big tin meat balls") that a detailed list was close to impossible. The non-food section included "Coal £10, HP on husband's suit and shoes £2": in many ways, 1982 had a closer relationship with Orwell's Wigan than it does with now. The constants stretching from 1936 the present were the quarter of the food bill that got spent on bread, pies and cakes; the complete absence of fruit; the meat ration confined to corned beef.

They were a plucky family. The wife loved Catherine Cookson's novels. "They make your problems look like nothing," she said. Who was I, who are we, to press on her recipes for stuffed carrots and 100 new ways with the baked potato? Yet one couldn't help feeling, like Orwell, that it was a shame, and that more than poverty was to blame – which must also be true now, because it can hardly be price alone that drives low-income families towards high-fat, processed food when the price of processed foods has risen by 36% over the past five years, more than any other food category. A fact may have to be faced: some people like it, and, given the huge power of the food business, coaxing them in a healthier direction may be no easier now than it was for society ladies in the 1930s.

My neighbourhood has some fine food shops: a cheese emporium, a greengrocer's, a well regarded butcher's and a recently opened fishmonger's. Walking past them the other day, I was suddenly struck by how much this Toytown high street depends not on old traditions but on money – the City money that has come to settle here. Visit any of these shops to buy something healthy, your weekly Eatwell Plate allowance of £16.70 will very soon be gone. A halibut fillet, a tiny pyramid of goats' cheese, a bunch of grapes … pfft! In the end, how can you describe this gulf between the rich and the poor, more extreme than in Orwell's day, other than to say it's wicked?