We live in the middle of urban Barnsley, not in some country idyll. And this couple certainly aren't right-on eco-evangelists. But they want their five-year old daughter to know where her food comes from, to appreciate what she puts in her mouth, and to take nothing for granted. If their hens don't lay, there is no scrambled egg for breakfast.

Rather than lecturing us about left-overs, the Prime Minister should also be thinking about where our food comes from. Our grandparents worried about quantity, about having enough food to put on the table.

Until now, most of us have had the luxury of worrying only about quality. But with global food shortages, climate change and the cost of fuel, the clock is going backwards.

I'm not talking about sourcing a particular cut of organic meat to a particular organic cow, but about accepting that the issue of food is now more important than at any time since the Second World War. We all need to get our heads around it, whether we are five or 55. Food has become scarce and expensive. All the signs are that it will become ever more so. There is no magic formula which will return the cost of bread and milk to what it was in 2006.

The Government has a role, indeed a responsibility, to guide us through the tough coming months. Never mind tips for making mincemeat out of the Sunday joint; Ministers need to turn around entrenched attitudes towards food production and consumption.

Western countries have upgraded food and fuel into national security concerns over fears that shortages could cause civil unrest. If that doesn't spell out that it's time to get serious, I don't know what will.

If food has the potential to create a national emergency, then surely it is more important than ever to know where it comes from. At the very least, we need to arm ourselves with facts about imports and exports, about the global buying-power of the supermarkets, and about bio-fuels and how their cultivation impacts upon food-growing.

On a more personal level, if we don't appreciate how our food starts out, we can't possibly appreciate its importance when we eat it. As a nation, we have a very long way to go.

If you want to see sheer thoughtless greed, check out the customers at an "all-you-can-eat" buffet. It's all very well Gordon Brown going on about how scoffing up our scraps will save us £8 a week, but just how far removed is he from the laden tables and discarded half-full plates of a typical all-inclusive holiday resort? Has he ever seen those already-obese kids piling their plates with chips and onion-rings and burgers?

He must find the courage to challenge that kind of arrogant attitude before he picks on the already cheese-paring housewife, or, indeed, house-husband; it's typical of him to go for the easy target first.

On his own all-inclusive G8 break, hours after his "waste not, want not" speech, Brown and his fellow world leaders toyed with six courses at lunch, followed by eight courses at dinner, including caviar, smoked salmon, Kyoto beef and a "G8 fantasy dessert". I would like to have seen the overflowing kitchen bins after that lot.

It is clear that food supply is a global problem – despite the rotten example that is set by world leaders. Although it requires a coherent international response, it also requires action at national, regional and local level. We need go no further than the 150th Great Yorkshire Show this week to remind ourselves of the crucial role of British farmers.

Behind the handsome show cattle and prize produce is the lifeblood of Britain. Without our farmers, we would be even more reliant on imports than we are now; we produce only 60 per cent of the food we eat, down from 74 per cent in 1994.

We owe it to farmers – and to our country – to support them, to vote for those who will favour trade policies which will help them, and, whenever possible, to buy local food locally and in season.

The link between grower, seller and consumer demands more than lip-service in a one-off supermarket promotion. It must become the bedrock of our food industry. The good news is that a change in our shopping habits is coming of its own accord: the shelf-life of the £200-plus weekly supermarket shop is running out, simply because few of us can actually afford to do it any more.

We are being forced to shop only for what we need, not for what we want. But this is just the start. Understanding where our food comes from could, in the not too-distant future, become a matter of life and death.