A strange thing happened yesterday morning: I found myself in wholehearted agreement with Gordon Brown. His comments urging British consumers to stop wasting food came after a new Cabinet Office report discovered that British families are each throwing away food worth an average of £420 a year. Put it all together and that's more than £1 billion worth of groceries going uneaten annually. Instead, it's left to fester in wheelie-bins and then landfill, preying on our consciences and draining our bank accounts in the process.

This report does not tell us anything we did not already know - that a great many people are throwing away an awful lot of food. It is commonplace these days, and doesn't seem abnormal; we just think, “Oh well, out of date, I'll chuck it.” And we do, with only the vaguest flicker of regret. What these figures will do, I hope, is jolt some people into thinking again about the way in which they shop, cook and eat. Not necessarily out of environmental considerations, but out of something far more compelling: the desire to save money. Can you really afford to throw away £420 a year?

Housekeeping is the art of provisioning your household and serving up interesting and economical meals for a family. And it is a skill in decline. If you're not in the habit of it, planning a weekly shop that covers all the bases but doesn't leave you with a huge surplus can seem like too much bother.

It feels archaic, a burdensome duty that can be sidestepped easily enough by purchasing ready meals or chucking some chicken breasts into your basket on the way home. Look in any city centre supermarket during the evening: it will be filled with young professionals queueing to buy obvious ingredients for that night's meal. Eighteen months ago, I would have been in the queue too: I was a kitchen cynic.

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I hated the responsibility of shopping and cooking for my husband and our two children. It was unwanted drudgery. So I went on auto-pilot, buying similar food every week. If we wanted anything special that meant another trip to the shops, where I'd buy in a frenzy to compensate for not having really thought through what I was doing. Result? More wasted food, higher grocery bills. I'd be spending up to £100 a week on food shopping, and throwing out a fair proportion of that food at the end of the week.

Now, though, I spend between £50 and £60 a week, my family eats better, more interesting food, there is no waste and - best of all - we've become much more hospitable, inviting friends around for dinner much more often than we did before. The transformation happened because I have been co-writing a book with chef Rosie Sykes and food expert Polly Russell, acting as a glorified guinea-pig.

Between us we have devised The Kitchen Revolution, a cookbook with planners, shopping lists and recipes for every day of the year. It relies heavily on creative use of leftovers, using store-cupboard foods, and cooking in bulk so that you can have home-made ready meals tucked away in your freezer for those nights when you lack the will to set-to with your oven. The book is extremely detailed - it was written for numpties like me - but researching it has taught me a few wider housekeeping rules that have completely changed my relationship with food and cooking.

Rule 1: Learn to love your leftovers
Don't see them as negative, curled-up reminders of food you didn't get around to eating. Leftovers are treasures that make your life easier and save you money, time and energy. Because they have already been cooked, half the work has been done for you. All you need is a little creative forethought. You have to interpret them into other dishes. For example, below are three recipes. First there is what we call a “big meal from scratch”, a rather delicious roast leg of lamb with braised lentils and carrots. Then there are two other recipes, both of which incorporate leftovers from the first. Take the carrots: these look limp and unprepossessing, but add the leftover roast garlic from the lamb to give them a new, delicious richness. Combined with some peas from the freezer and other ingredients, they become the heart of the second dish. And you don't have to worry about starting a new meal, or even shopping for a new meal, from scratch. So much of our food is pre-packaged that some people seem to recoil from the idea of eating rough and ready old leftovers. Well, don't: using them is a revelation.

Rule 2: Buy seasonal foods
I always thought foodies were just being precious when banging on about this, but I have to admit that they were right: seasonal food tastes better and it's cheap. Look up a list of seasonal foods and try buying some of July's entries - you'll see the difference too.

Rule 3: Know, and use, what's in your store cupboard and your freezer
I make sure I have the ingredients of my favourite “larder feast”, as I call store-cupboard dishes, in stock at all times. It's a lentil and chorizo stew that may not sound entirely gourmet, but is delicious and takes about 25 minutes to put together. Now we can invite friends around off the cuff and there is no need any more to do a last-minute shop. Best of all, I'm basing my meal on 29p cans of lentils, not extraordinarily priced chicken breasts.

Reading them back now these three bits of advice sound almost laughably simple. However, before I made them part of my domestic life I was one of Gordon Brown's wasters, and I lacked the knowledge to change.

Nobody wants to be told what to do all the time. Certainly our book isn't supposed to be dictatorial - we want people to take the ideas and recipes and adapt them as they wish. And we all have nights when there's nothing better than the sound of the pizza man's moped pulling up in front of your door.

But there is a decadence, even a wantonness, about the way so many of us feed ourselves now that is clearly unsustainable. Remember, £1 billion worth of food a year, thrown away uneaten. The only people that's good for are supermarket shareholders.

Embracing leftovers, seasonal food, and store-cupboard cooking - the basic precepts of good, old-fashioned home economics - will take some of that money back from their income streams and return it to your pocket. Then you can spend it on something really wanton.

The next step: cook one - get two free
Forget about “buy one, get one free”: as Gordon Brown would tell you, that just leads to waste, and throwing out food at the end of the week. This way you can treat the whole family to delicious roast leg of lamb with new season's garlic, braised lentils and glazed baby carrots - and with the leftovers, you can create two more tasty dishes on succeeding days. In this recipe lamb is roasted slowly on a bed of fresh garlic until both have become meltingly soft and sweet. Garlic fresh from the ground is known as wet garlic and has a milder flavour than when the bulb is dried. It looks similar to ordinary garlic except that the bulb tends to be bigger and the skins are softer and slightly moist; they often have a faint purple tint. In this recipe the bulbs are roasted whole until soft. The cooked garlic pulp can then be squeezed out of the cloves by everyone as they eat.

Roast leg of lamb with braised lentils and glazed baby carrots

Spiced lentil salad with hoummos and lamb

Braised summer vegetables with pancetta and sherry

From The Kitchen Revolution, by Rosie Sykes, Polly Russell and Zoe Heron, Ebury Press, £25. Available from Times BooksFirst for £22.50, free p&p. timesonline.co.uk/booksfirst

For more recipes and advice on saving time, effort and money in the kitchen go to thekitchenrevolution.co.uk

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