I had my first food 'awakenings' in the 1980s and 1990s. I lived, for a year, in France, where food is treated with a reverential seriousness that frequently borders on the obsessive; and some of this obsession rubbed off on me. In Britain, I had enough money to be able to eat in smart restaurants from time to time. I talked knowledgeably (or so I thought) about foie gras and asparagus; about fine cheeses and fusion cuisine. And, like everyone else, I bought lots of big fat glossy cookbooks, filling my shelves with what I'm not ashamed to describe as 'gastro porn'.

Despite this active interest in the business of fine eating, a couple of years ago I discovered an enormous hole in my food knowledge. As I say in Seasonal Food, I think it was prompted by a discussion of asparagus, which is as famous for the brevity of its season as it is for its eating quality. As a fully-paid up member of the foody brigade, sometime frequenter of Michelin-starred restaurants and farmers' markets, I hadn't a clue when its season was. This was a bit embarrassing, if nothing else: don't know when the asparagus season is, I thought? Pah! Call yourself a gourmet?

The obvious thing to do was go looking for a reference book. After all, with so many lovely food books our there, there's bound to be one on seasonality. But there wasn't. There were plenty of seasonal cookbooks, some of them classics of the last few decades: Margaret Costa's the Four Seasons Cookbook, which was one of the first cookery books to concentrate on simple, seasonal ingredients; Delia Smith's summer and winter collections; The River Café Cookbook Green, a great veg-based seasonal tome. But none of these answered by simple questions: what's in season, when and why?

So now two questions started to nag at me. Why did I know next to nothing about the seasonality of food, despite fancying myself to be a bit of a gastronome? And why aren't there any reference books? The first reaction was the obvious one: maybe it's just me! Maybe I am uniquely ignorant; the only one who wasn't concentrating during seasonality lessons. And maybe there aren't any reference books because everyone else just intuitively knows about it! Some quick questions to friends and fellow foodies happily dispelled this notion, but revealed a surprising fact: seasonal ignorance was a pandemic. Very few people could tell me what's in season when. It seemed that you needed to be either a) a farmer or serious vegetable gardener b) a professional chef; or c) over 60 to have the least idea of British food's seasonality. My straw poll is backed up by a Safeway study cited in Joanna Blythman's supermarket expose ''Shopped', which revealed that in 2002, 88% of respondents didn't know when certain favourites are in season. (The irony that supermarkets, as we shall see, bear much of the responsibility for this ignorance was lost on the author: and it's not lost on me, either).

So the first question suddenly got bigger. Why do most people - some of whom have read all the cookbooks and eaten the finest food -- know very little about food and the seasons? What's going on? At first I thought the chefs and food professionals were keeping the knowledge to themselves deliberately, throwing the occasional mouth-watering but unexplained tidbit to us salivating punters (like 'now, of course, the lobster is in its prime') in order to keep us in thrall to their expertise. This sort of stuff was just staring to irritate me, though: why is it in its prime? How long does its prime last for?

Ultimately, though, the reason there are seasonal reference books is not down to a conspiracy of chefs and foodwriters. It's more to do with the fact that for these professionals, food seasonality is second nature. They mostly have seen no need to explain it to us.

The background to the pandemic of ignorance about food and the seasons is more complex, though; and much more interesting. How could it be that a nation that worships at the altar of celebrity chefs, that eagerly devours gastroporn, is missing out on one of the key pieces of information that determines how good something is to eat?

Cross the channel to France, and there's an interesting inversion. Most French kitchens have little need for bookshelves, containing few, if any cookbooks. But French cooks - male and female - will tell you what's in season when without batting an eyelid. They'll produce great meals without recourse to complex, multi-stage recipes framed by mouth-wateringly arty photography. And in rural areas, having a 'potager' (or small vegetable garden) is second nature, not, as it is in Britain, a massive project necessitating the purchase of yet more glossy guidebooks. I once took a French newspaper executive to lunch in a restaurant with a regional French theme. He hooted with derision when served watermelon, which was not only absent from the cuisine of the region the restaurant purported to represent; but was also out of season. Then he started giggling at the wine which, bizarrely, was stored up by a sunlit window. You have to be extremely careful where you take French people to lunch.

So why this difference between Britain and France? History. The origins of our seasonal ignorance go back several hundred years, back to the acts of enclosure which, from the 16th century onwards, reduced the amount of common land on which people could graze livestock and grow land. By 1750, food historian Colin Spencer notes that most agricultural land was held by a few thousand landowners, and the smallholder who grew and raised his own food had become a rarity. We began to lose our connection with the land early in Britain. And then our industrial revolution - the first in Europe - meant that people moved into towns and cities in huge numbers and became less and less involved in - and aware of -- nature's cycles.

Fast food, far removed from nature's cycles, is not just a contemporary phenomenon: as Spencer points out, the diet of industrial workers often 'declined to little more than bread, tea, jam and sugar': a distant relative of the quick-fix, carb, sugar and caffeine-laden diet that is wreaking such havoc today. Incidentally, William Cobbett, who railed at the worsening lot of the landless farmworker in the 18th century, reserved much of his considerable store of vitriol for tea: he saw it as an evil, worthless beverage whose lengthy preparation (involving, in those days, much setting and cleaning of fires) sapped the strength of honest peasants who would have been much better off drinking their own homebrew. Personally, I can't help but agree with him.

The tea problem apart, Britain's land enclosures and industrialisation weakened our relationship with the land and its cycles earlier more severely than anywhere else in Europe. The seeds of my seasonal ignorance were sown many years ago.
Britain had a brief flirtation with its distant peasant past during the 1940s, when the strictures of war sent many back to the land, their allotments and their back gardens to grow and raise their own food. Several commentators have pointed out that nutritionally, this was one of the healthiest points in our history. But after the war, galvanised by the drudgery of rationing and the fear of not being able to feed ourselves as a nation, Britain turned to industrialised, chemical agriculture as the solution. Apart from what we now know about the environmental impacts of this type of farming, it removed yet more people from the land. In the 1950s, there were nearly half a million family farms; today, there are just over 200,000; and 23,000 of these produce half the food we eat. Just 1.8 percent of our workforce is engaged in agriculture, the lowest rate in Europe. An unavoidable consequence of this is that culturally, we know less and less about the origin of our food as its production becomes progressively more and more mechanised. Anyone seen a farmer recently?

History has conspired to keep us away from our food chain; and this is one of the main reasons why if you stop people on the street today and ask them when the apple-picking season is, you'll get some funny answers (OK, maybe not if you ask this question at an Eden Friends' gathering during Organic Week!).

But the biggest and most recent contributors to our pandemic of ignorance about seasonal food are the supermarkets. In her excellent new book 'Shopped', campaigning foodwriter Joanna Blythman coins the term 'permanent global summertime' to describe supermarket shelves that are filled with the same cornucopia of fresh produce, all year round. It is, of course, to the good that we no longer have to stave off scurvy by eating nettles in March, as our ancestors did after a winter deprived of green stuff. Or that we don't have to worry about near starvation in the 'hungry gap' from April to June when stored produce was exhausted and the new stuff was not yet ready. But do we have to eat green beans all year round? Must we - as I ask in the title of this talk -- have strawberries for Christmas? And as for 'grown for flavour' tomatoes in the depths of winter - don't get me started. What else, apart from flavour, were they planning to grow them for? Suitability as a reindeer's nose?

The supermarkets argue that this year-round predictability is what customers demand, just as we apparently will only buy dead-straight courgettes, or apples whose diameter only varies by a few millimetres. They may be right: but this is a demand that has been manufactured. Over the last couple of decades, shoppers have become steadily accustomed both to the permanent availability and to the physical perfection of produce, as the supermarkets use these as marketing tools to gain advantage in their hypercompetitive world.

If you put the question this way: 'Would you like fresh strawberries all year round?' most people will of course say yes, just as they would if you offered them cheaper petrol or a free flight. But what if you revealed to them the price of what I might call 'permanent global strawberries', buy putting the question this way: "We could give you fresh strawberries all year round, but bear in mind that for nine months of the year they won't taste of much. They'll have been raised artificially, of course, often with artificial heating that pumps greenhouse gases into the atmosphere, and in huge fields of polytunnels that blight the countryside. Oh, and mostly there'll just be one variety, that's not too bland but good at standing up both to refrigeration -- which, of course, makes them taste blander still -- and to the long journeys by lorry or plane which they will all have taken. How about some nice apples instead?

Today, many shoppers still don't know about the hidden cost of food out of season; and, thanks to years of permanent global summertime, many have forgotten the real taste of food that's grown naturally, locally, and in season. It's time to start fighting back and reclaim the fantastic seasonal food we have been losing.

Journalists such as Joanna Blythman and 'Not on the Label' author Felicity Lawrence have done much to bring the cost of the modern food chain to public attention. They show that the current attempt to erase the seasons is part of a broader erosion of choice, in which ever-larger producers and retailers are slowly squeezing the life out of food diversity and local communities. The fact that this is presented to us as an expansion of choice is not without irony. As many of us are now realising, a choice that may ultimately be between Wal-Mart or Tesco is no choice at all, neither for farmers nor for shoppers.

But as well as exposing the downside of today''s food industry, we can fight back against it by publicising the positive benefits of doing things differently. To paraphrase the rallying call of the World Social Forum: 'another food chain is possible.'

Discussions of better, healthier ways to grow food have been getting louder ever since Rachel Carson wrote 'Silent Spring' in the 1960s to highlight the impacts of chemical agriculture in the US. Today, organic production is seen by all except those with a big axe to grind as a healthy, positive (if relatively expensive) alternative; and something that can help the environment too, for example with crop rotation and less use of fossil fuel.

There's also been a resurgence of interest in local food, with farmers' markets growing rapidly around the country and local food accreditation schemes like 'Local to Ludlow' making it easier for people to buy food from just around the corner.

Eating seasonally is not only a way of getting better food; it's also a positive way of moving us towards a food chain that benefits shoppers, farmers and communities, not just huge multinationals and middlemen.

So here's seven reasons why eating seasonally is a good idea.

1. Food tastes better in season. What's true for strawberries is also true for loads of other things: winter root vegetables and brassicas that are improved by frost; hill lamb that has had a slow start grazing on spring pasture, rather than a diet of concentrates in the chill of winter; fruit and vegetables like plums and tomatoes, whose sugars have been developed to a perfection of ripeness by late-summer sunshine; wild game that has had a rich autumnal diet and plenty of outdoor exercise. There are just a few examples; there are many more tasty reasons for eating seasonally.

2. Food is better for you in season. Scientists and nutritionists in the audience might rightly jump up now and say prove it! I can't; it hasn't been proved, empirically. But there's a few factors to consider. Fruit and veg such as broccoli are touted for their high nutrient value; but in many cases, particularly broccoli, this value degrades rapidly over time. Seasonal food is more likely to be local; and local food wiil have spent the minimum time on the road. So sometimes, seasonal food is healthier.

3. Seasonal food is better for the environment. If you believe that human activity contributes to climate change - and even George Bush seems finally to have come round to the idea - then buying airfreighted French beans from Kenya in the winter is, frankly, daft, given the vast amount of greenhouse gas produced by such unnecessary trade. Especially when there's so much great local veg around in winter. Seasonal food doesn't need the artificial heat and light needed to create a year-round growing season in a temperate climate like ours. And seasonal food fits into traditional systems of farming, which don't need the same energy-intensive inputs of pesticides, herbicides and artificial fertiliser as intensive systems.

4. Seasonal food is cheaper. The most extreme example has to be blackberries, which goad me into a Radio 4 listener-type rant: 'Why oh why oh why do people even contemplate paying vast sums for imported blackberries out of season when, for up to three months of the year, they're in huge abundance, and completely free!' Surely the jams and jellies we can make with them will compensate for their absence for the rest of the year? Crop permitting, almost anything that's in season will be plentiful and therefore cheaper. Even Evesham's aristocratic asparagus is affordable to all of us in a good year.

5. Seasonal food supports local agriculture. Whether it's from the farm down the road or a specialist producer a few hours away, seasonal food that suits our climate is more likely to have been grown here. Buying locally offers another market for beleaguered food producers, who are often squeezed between the impossible demands of supermarket buyers, and cut-priced competition from overseas.

6. Seasonal food makes you think about preserving stuff. Faced with a massive glut of fruit and veg, what do you do, just freeze it? Or even throw it away? Not likely. Jams, chutneys, jellies, pickles preserves, even -- for those fortunate enough to keep their own pigs - bacon: all of these were invented as ways of preserving a seasonal surplus. And all of them create new foods, whose origins are in the seasons, but which can keep reminding you all year round of the fleeting seasonal treat from which they originated.

7. And finally, seasonal food brings variety into our lives. Who wants to eat the same things all year round? I like having to wait for stuff. The anticipation of the first forced rhubarb from Yorkshire; licking my lips at the prospect of rich autumnal game and mushroom feasts to come; looking forward to summer sardines. There is always a seasonal treat to look forward to in Britain: and once you know what they are, they change the way you eat and shop - even the way you order in restaurants -- and turn each month, even each week, into a gastronomic adventure. A year is just long enough too forget how good it was last time, so that's 12 months of food surprises.

Tastier, healthier, greener, cheaper, supporting local producers, inciting jam-making and bringing you constant variety. Eating seasonally makes a lot of sense.

But how can we eat seasonally in the age of permanent global summertime?

The first step is simply to be aware of the seasonal cycle of food, a sentence from which you would rightly infer a shameless plug for my book.

The second is to consider different places to go looking for food, something which more and more people are starting to do. Supermarkets do sell British seasonal food, but it will almost always have made the tedious trip from grower to packhouse to distribution hub before it finally gets into your local store. This means, incidentally, that the strawberries grown in the field next to your town may have travelled hundreds of miles before returning to the supermarket nearby, one of the many farcical facts of our food chain.
As a result of all this travelling, supermarkets choose varieties that can put up with this treatment, often making sure that produce is picked before optimum ripeness to make it even hardier. So fewer varieties, and less-than-perfect ripeness.

If you're fortunate enough to have good, local shops - then the greengrocer, butcher, fish and cheesemonger will all give you the best chance of eating produce which is in its prime and has shortest amount of time travelling from plot to plate.

Although it seems unbelievable in a time of seasonal plenty like September, there are plenty of places, especially in some rural areas, that don't have good local shops; where the only option is the supermarket. In this case, it's also worth seeking out your local farmers' market if there is one: there are more and more throughout the country, and I always see it as ironic, yet of course fortunate, that where I live in inner London, far from the fields, I have several to choose from each week. The National Association of Farmers Markets has a good list at www.farmersmarkets.net. Another good reason for visiting farmers' markets is the sheer range of produce you will encounter, from unusual varieties of fruit to rare breed meet.

Then there are vegetable box schemes, also on the increase, and which mostly pride themselves on delivering seasonal, local, and usually organic produce.

Finally there's the grow-it-yourself options. Ultra-serious gardening gourmets like Monty Don claim that growing your own is the only way to experience the true freshness of seasonal produce that deteriorates really quickly, like beans and peas: he even suggests having a pan on the boil before you pick your own sweetcorn. Given the superb quality of some of the farmers' market sweetcorn I've eaten this season, this seems a little excessive. But there's little to match the quality (and the thrill) of picking your own tomatoes off the vine on a hot summer's day, or wandering out on a dark winter's evening to pick some fresh kale for a warming soup. Even the smallest garden - as our tiny London plot testifies - can produce quality and variety (if not much in the way of quantity!)

Local shops, farmers' markets, box schemes, growing your own: My family has been doing a combination of all these things in a quest for the finest seasonal produce. And they've transformed the way we eat. Food is 'selon le marche' - according to the market - rather than a repetitive weekly filling of a trolley. And whilst, yes, it can be dull in the old 'hungry gap'; and yes, I fume when the box scheme sends antipodean apples rather than stored British ones; and please, not cauliflower again…..Despite all this, it is a much more interesting and healthy way to eat. And it doesn't seem more expensive either.

In researching my book, I set out to learn what's in season, when and why in Britain. In doing so, I learnt an awful lot more besides about food in Britain. And whilst there is so much that is mouth-watering and heartening -- such as this celebration of food at Eden -- much of what I learnt disturbed me. It seems we've reached a bit of a watershed with food in this country. As Felicity Lawrence points out, it's going to be difficult to row back from a food chain that is becoming increasingly mechanised, automated, fuel-dependent and concentrated in the hands of a few owners who wield enormous power over what we eat. The forces of blandness, homogenisation and permanent global summertime seem unstoppable.

But there is a way to avoid this grim, corporatised food future. And many are starting to express their resistance by producing and buying food that is genuinely fresh and distinctive, and grown and raised traditionally.

When I started to think about food's seasonality several years ago, it never occurred to me that buying an in-season tomato direct from the grower could be a political act. But it is: and millions of little transactions like these, happening more and more often, are part of what's needed to give us back a sustainable food chain that benefits everyone, not just a handful of rich retailers.