The cry in our house this week has been: “Waste not, want not!” in our best Fife accents. And yesterday I carried out a stringent audit, armed with my digital scales and an edict banning anyone throwing away anything edible without first passing it by me. What I found is enough to confirm the Prime Minister's darkest fears. We are wasters.

Breakfast: it went well enough, mainly because of an in-house recycling scheme whereby my wife eats the crusts of the children's toast. Gold star to her. Wastage: the puddles of milk and scraps of Weetabix at the bottom of the bowls. One piece of toast that I burnt. By weight, 10 per cent of our breakfast was thrown away.

Lunch: taken at the Edinburgh Royal Botanic Gardens café as sandwiches for the adults and 250g each of Dinosaur World lunchboxes for the kids (55g of that was packaging). One of them passed on the cheese roll, and I don't blame her. Wastage: 30 per cent.

Children's supper: they had chicken, peas and sticky rice. The three-year-old left half of hers. I ate it. Wastage: nil.

Adult supper for four: Thai lamb salad, sticky rice, vegetables, strawberries. I threw away about half a kilo of vegetable offcuts - the inedible ends of asparagus stalks, onion skins, eight lemon and lime husks. But that doesn't count - it's organic wrapping, isn't it? And it went into the council compost bin. So did 500g of rather tired Scottish strawberries that I dressed with red wine. They were only picked at. When I snatched my friend's bowl and weighed it, she told me I was sad. Wastage: 15 per cent.

Clear-out: during the day four yoghurts, one baguette, one withered Durrus cheese, half a bowl of pasta and an ancient pack of pig's trotter in jelly that I got from the chef Fergus Henderson all went into the bin. That was a kilo. So at the end of the day we and the two supper guests had eaten about 5kg of food. We'd thrown away about 1.5kg that could have been eaten. That puts us in the same league as Gordon Brown's average British wastrel who, if you believe the Government's waste campaign, WRAP, throws away 30 per cent of all the food he or she buys.

This is serious, and we need to do something about it. But I'm not certain that what needs to be done is as simple as the Prime Minister suggests. If you go back to the WRAP report on which the Cabinet Office's food strategy document is based, you find out some fascinating things. Of the 4.1 million tonnes of edible food that we throw away, the most significant item (by weight, not price) is potatoes, followed by bread. We throw away more salad than we eat - 60 per cent of it, by cost. The main reason for throwing this food away is that we had too much on our plate (1.2 million tonnes), followed by food being past its sell-by date (800 million tonnes) or looking, smelling and tasting bad (750,000 tonnes).

But there's a glaring gap in the WRAP report. It doesn't mention how much food is wasted before it comes into our homes. You have to look elsewhere for that, to a report by the Government's watchdog, the Sustainable Development Commission. This was published last February and pretty much buried: it claimed that 1.6 million tonnes of food was wasted by retailers, who chucked out more good food in their packaging and processing systems than we did at home because it was past its sell-by date or unhealthy.

Brown hardly mentioned the food retail system's excesses and inefficiencies in his speech, except in, rightly, questioning the discount offers that encourage us to take home more than we need. Yet the supermarkets waste food far more lavishly and for much worse reasons than we poor house-spouses. They overorder fresh produce because they can pass the costs of disposal back to the supplier. They reject up to 60 per cent of perfectly good vegetables because they do not fit exact shape and quality standards. They bully us with daft use-by dates. And, worst of all, in meat processing as much as a third of the edible tissue of animals is discarded because it doesn't meet the supermarkets' narrow definitions of the sellable. Kidneys, anyone?

So why did Brown not wag his finger at the supermarkets? That's not something that Jack Sprat can speculate about. But let's hope that the next time Lord Sainsbury of Turville, who has given £8 million to the Labour Party since 2002, comes to tea at No 10, Gordon Brown makes him show a clean plate afterwards.

alex.renton@thetimes.co.uk

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