RASPBERRIES, blueberries, peaches and nectarines: did you eat any over the festive season? Not long ago that would have been a stupid question, for these were fruits of high summer. But global fruit buying has turned the world upside down.

From early December, supermarket shelves fill up with precious cargo air-freighted from the southern hemisphere and tropical countries. The goal is to capture the luxury festive market, when consumers can be persuaded to dig deep into their pockets for 'out-of-season' specialities such as apricots or blackberries. This southern hemisphere trade continues until May. Air-freighting adds an estimated 70 per cent to the cost of the produce. But if you want plums or asparagus for a dinner party in April, that infamously lean month for interesting fruit and vegetables, you can have them - at a pretty steep price.

Purists are suspicious of all this. They suspect foul play, genetic engineering, produce coaxed to grow in an artificial environment - in short, unhealthy tinkering with nature.

But the trade is far from sinister. Southern hemisphere countries have their summer during our winter, and as long as affluent northern hemisphere consumers are prepared to pay the price of flying the harvest over, there is no earthly reason why items such as raspberries and cherries cannot be available everywhere all the year round.

Historically, South Africa and New Zealand have provided the bulk of southern hemisphere supplies to the United Kingdom. But South Africa has had its problems: apartheid leaves a bad taste in many people's mouths, and boycotts do not aid trade.

Add to these political issues the fact that South Africa was almost exclusively associated with citrus, Granny Smiths and the sort of dull, pippy grapes you used to take to invalids, and the result is an image problem. New Zealand is altogether more acceptable for many British consumers, but a strict diet of apples and kiwi fruit is not.

One southern hemisphere country which is rapidly reprogramming the fruit and vegetable expectations of British shoppers is Chile. While British consumers now take for granted one-off items such as Kenyan green beans and Guatemalan mangetouts, the sheer range of risky, highly perishable produce on offer from Chile is astounding. It encompasses most interesting green vegetables, notoriously difficult berry fruits and stone fruits of all kinds. And last but not least, several sweet and juicy varieties of seedless grape.

All this is by virtue of Chile's fortuitous geographic setting. It is the world's longest country, a thin strip of land stretching almost 4,000 miles from Peru in the north almost to Antarctica in the south. That means that within Chile, growers can chase summer around for half the year, starting in the north in November and moving south.

Apart from the sun, another asset is the country's natural barriers against pests and disease. The Atacama desert protects Chile in the north, the Pacific Ocean laps the west coast, and to the east lie the mighty Andes. All this combines to produce the sort of horticultural environment, complete with several micro-climates, of which supermarket produce buyers dream.

Chilean produce, although relatively new to Britain, is familiar to Americans. The United States, particularly the Californian coast, has been Chile's main market. For US horticultural imperialists, Chile has been a fertile back garden. Nowadays the growing sophistication of British consumers is presenting a market that Chile is only too happy to tap.

And it is such sophistication that has allowed Chilean growers to steal a march on their competitors in the southern hemisphere. The US west coast is a discerning food market that Chile has become adept at servicing. To export produce there, you need to follow stringent Food and Drugs Administration guidelines on quality and safety, and satisfy the knowledgeable American consumer on issues such as pesticides. You also have to offer the variety of produce that affluent Americans expect.

Grapes are a perfect example of how Chile has kept a step ahead of the pack. Consumer perceptions of South African grapes have been rudimentary: either they're black or they're green. But Chile has introduced us to a variety of names, such as Flame, Thomson's and Perlette, that do much more to excite the palate.

A Sainsbury's representative puts it this way: 'Until the end of the Eighties, South Africa thought it was the bee's knees. It could dictate the market price for grapes and sit back. Then Chile came along with much more interesting American varieties. Now South Africa is reacting. People don't want seeded grapes any more, but it takes time for established producers to change.'

The Chileans have the advantage when it comes to flexibility, he points out. 'Unlike South Africa and New Zealand, where fruit buying is organised through two or three export boards such as Outspan or New Zealand Apples and Pears, Chilean fruit growing is in the hands of private companies or co-operatives. Although that means Chile loses out on economies of scale for generic promotions, it makes producers more adaptable when it comes to changing varieties, new ideas and so on.'

The American influence shows in other US classics such as Santa Rosa plums, Bing (sweet) cherries and blueberries. But is that necessarily a good thing? Although American produce is notorious for looking great and tasting of nothing, Marks & Spencer is convinced that Chilean produce more than meets its quest for 'good eating quality'.

According to M & S fruit buyer David Gregory, if you insist on strict maturity standards at harvest, the fruit should taste as good as anything you get in a European summer. 'You take Chilean raspberries. We have them harvested almost when the plane is ready to take off. They are picked, rushed to the airport and are on the shelves within 48 hours. Think how long it takes for Scottish raspberries to be road-freighted (not necessarily chilled). It might not be much faster,' he says.

M & S also takes care to make sure that stone fruit, such as peaches from Chile, are properly ripened on arrival in chambers equivalent in temperature to the average domestic fruit bowl. The people who pay a premium price expect a premium product.

You may feel uneasy with the concept of out-of-season fruit and vegetables.

It may even offend your idea of the natural order of things. But you are likely to see more of them arriving on our shelves: strawberries from Zimbabwe, redcurrants and blackberries from Columbia, haricot verts from Kenya, Argentinian and Thai asparagus, Australian blueberries, Guatemalan peas. There is no stopping the southern hemisphere now, especially South America.

'We take the same basic approach everywhere,' says Mr Gregory. 'We identify the places in the world that can grow the produce we want. If it doesn't have its own management, we put it in. What we want is to be able to offer summer all year round.'