Twenty years ago fresh beans flown into Britain from Kenyan farms were labelled with an aircraft symbol to denote freshness and entice shoppers.

The symbol is now being resurrected for perishable goods such as asparagus, strawberries and grapes. But this time shoppers are being encouraged to leave the goods on the shelf if they wish to be green and help to reduce Britain’s carbon footprint.

The aircraft stickers will appear on produce at Marks & Spencer and Tesco from Easter. The logos are still being devised but the M&S version is likely to state “Flown” on the label whereas at Tesco the favoured phrase is “Air- freighted”.

The precise number of miles will not be declared. Supermarkets believe that it is sufficient to label the food so that shoppers can then decide whether they wish to buy the item.

It is important to note, however, that food imported by air may be more environmentally friendly than something grown out of season in a heated glasshouse in Britain.

Only between 3 and 4 four per cent of food sold in supermarkets is flown to Britain — the costs make this form of transport too prohibitive. Most imported food is shipped. But the issue is the latest battleground between leading supermarkets vying to be the greenest on the high street.

Asda is also working on a similar air sticker for fresh vegetables, fruit or salad items but it is also planning to tell consumers the number of miles that a product has flown.

A reduction in food miles, however, poses an ethical dilemma for supermarkets. Sir Terry Leahy, chief executive of Tesco, said: “There is a strong international development case for trading with developing countries. So the question is, should we shun Fairtrade horticulture from East Africa to save CO2, or champion it as an important contribution to alleviating poverty?”

To resolve the conflict Tesco hopes to reduce the amount of air-freighted food to less than 1per cent of produce and to ensure that there is a bias towards the poor.

The longer-term aim for the leading food retailers is to work out the carbon footprint for each product — though this could be some years away.

David Miliband, the Environment Secretary, has promised retailers that he will help to achieve this goal and has already commissioned academics at Manchester Business School to do a feasibility study about putting carbon footprints on food labels.

Tesco has agreed to commission other research to identify a universally accepted and commonly understood measure of the carbon footprint of every product that it sells. Each product will be analysed throughout its life cycle from production through to distribution and consumption. The aim is to allow customers to compare carbon footprints as easily as they can compare price or nutritional values.

Tesco has also allocated £5 million for the creation of a sustainable consumption institute.

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