As you tuck into your turkey and stuffing, pause for a moment and consider how it got to your plate.

You might be surprised to hear that the bird and trimmings could well have clocked up 24,000 miles.

One sample of a supermarket-bought Christmas dinner revealed the ingredients came from three different continents, travelling to the shelves by ship, plane and lorry.

Sustain, a coalition of 150 organisations campaigning for better food and farming, bought a supermarket chicken from Thailand that had been shipped 10,691 miles.

The same shopping basket had:

Runner beans from Zambia, airfreighted 4,912 miles
Mange tout from Zimbabwe, flown 5,130 miles
Carrots from Spain, trucked 1,000 miles
And potatoes from Italy, hauled 1,521 miles.

The sprouts were British but had already been on a 125-mile motorway trip to the supermarket's distribution centre.

Add another 925 miles to get it all to the supermarket where it was bought and our long-distance Christmas dinner has travelled a grand total of 24,304 miles - or once around the world.

Sustain policy director Vicki Hird said neither the environment nor society could afford the present system of long-distance dinners.

She said climate change was being accelerated because of the amount of fossil fuel being burned transporting food.

Any shortage of oil could quickly translate into a shortage of food, too.

During last year's relatively minor fuel crisis, it was only a week before supermarkets began to run short.

Longer term, the effects of all that carbon dioxide - the chief cause of climate change - being pumped into the atmosphere could fundamentally alter where we can grow food, and how much of it.

Ms Hird said: "It is quite a big beast to reform but we need to start insisting on initiatives like farmers' markets.

"We need to start now, because we can't wait until the crisis hits. The industry must be asked to rethink how it is doing things."

She said agricultural subsidies should be directed towards regional and local supply chains and more sustainable production methods, such as organic farming.

Airfreighting of food to Britain has increased by 50 per cent since 1978.

Sustain calculates that for every two kilogrammes of carrots flown in from South Africa, 11 kilogrammes of carbon dioxide are released into the atmosphere.

Every five kilogrammes of vegetables trucked in from European countries releases seven kilogrammes of carbon dioxide.

Organic food fares no better, with the boom in demand fuelling more and more imports - again often by air.

Once at the airport or the Channel ports, the journey has not ended.

Food distribution now accounts for between a third and 40 per cent of the freight on British roads.

Lewes organic farmer Martin Tebbutt said: "It would be interesting to know what the cost to society is, in terms of congestion and ill health, of all that food being carried about."

The bread sold at his organic farm shop at Clayhill, for example, is made from wheat he grows and mills himself. He sends it to a bakery in Newick.

His beef is from locally-reared cattle, slaughtered at Heathfield. Neither bread nor meat has travelled much more than 20 miles.

When Sustain went to a farmers' market in London to buy the ingredients for a Christmas dinner, the most-travelled part was the turkey, which had been brought 76 miles by van.

The carrots, cabbage, potatoes, sprouts and parsnips had travelled a total of 300 miles - making a total of 376 miles.

Mr Tebbutt sells apples from Robertsbridge, although he does sell broccoli that was produced in Portugal, a casualty of Britain's chronic shortage of home-grown organic food.

He said: "I should imagine if you went through the average punter's shopping bag coming out of a supermarket, it would be about 500 miles, ignoring things like rice, which you can't grow here. I think it is madness really."