Food miles are a measure of the distance your meat and veg travels enroute from field to dining table. It's becoming an issue because food and other agricultural produce now account for nearly a third of goods transported on our roads. Carrying all this contributes substantially to global warming.
Food travels further these days partly because supermarkets have replaced local and regional markets. The result is that milk ,eggs or apples can be transported long distances to a central depot and then sent miles back to be sold close to where they originated. The food processing industry isn't helping the problem, since many ingredients are sent around the country from factory to factory before they reach the shops.
We also import more food: 95 per cent of the fruit, and half of the vegetables in the UK are imported. Strawberries, for example, are flown in from southern Africa out of season. Unfortunately air transport is far worse for the environment than sea or road transport.
We are also responsible for food miles - most of us now travel further to buy our shopping and we usually go by car. Figures suggest that each year the average UK shopper drives more than 130 miles for food, usually to large, out-of-town supermarkets.
This isn't only bad for the environment - it helps destroy our local high streets too. Campaign group Friends of the Earth fear new planning guidelines will encourage even more out-of-town shops that will mean more car travel and the continued destruction of the high street.
What can you do? Try to shop on your local high street, at farmers markets or farm shops. Simply walking to high street, when possible, and buying fresh ingredients to cook at home will have an impact. And you won't always pay more: A survey by Friends of the Earth found that apples were cheaper in greengrocers than supermarkets. Another study found that street markets in London were "substantially cheaper" than supermarkets for fruit and vegetables.
If you must use supermarkets, check the labels on the produce you buy. Can you get English apples rather than those that have travelled from New Zealand, say?
Buying organic can also help. According to the Soil Association organic farming cuts down on the fossil fuels used to manufacture and transport the chemicals used in mainstream agriculture.
There are a number of initiatives aimed at improving local food in the UK, at both a regional and a local level. Sustain, the alliance for better food and farming, is piloting projects to get local food into local schools, hospitals and shops and there's the Shop Local First campaign.
A complicated picture
However there are other issues. By buying British you could be damaging the economies of developing countries where some produce originates. Sometimes fruit or veg grown in warm countries and flown here releases less carbon than British equivalents grown in heated greenhouses. It is less environmentally friendly, say, to grow British tomatoes out of season than it is to import tomatoes from Spain. The problem is that the energy needed to heat the glass houses in Britain is more than the energy used in transporting tomatoes from Spain, where no heating is needed.
Some supermarkets have announced that they plan to label products to give an indication of the amount of carbon released during production and transportation. It's an ambitious plan that could cost many millions of pounds, but it could help consumers make a choice.