And just how positive for the planet is your sausage roll?

Students at Sheffield Hallam University have been researching the environmental impacts of a range of everyday food products, such as the strawberry tart and the high street-bought sandwich.

They are hoping their findings might be included as part of a new system of food labelling, which could rate the carbon footprints of products in a 'traffic light' system.

The students traced the supply chains of their selected foodstuffs, calculating the carbon emissions of each stage of their production.

Their work, part of Hallam's £1.3 million Food Innovation Project, went all the way back to the growing of wheat to make bread, and the rearing of livestock to produce ham.

Next came the milling, drying and baking of products, all the way to the preparation of each finished foodstuff.

Their results showed that each sandwich or sausage roll has a footprint of between 14 and 34 grams of carbon dioxide.

Project member Dr Wayne Martindale said the good news was that the food chain was generally highly efficient whether it was using livestock or vegetable products, or whether production was organic or not.

"But there is scope to improve energy efficiency at all parts of the food supply chain," he said. "At a global level feeding six billion people is only possible if we maximise efficiency in our food chain. We're all responsible for accounting for where we buy our food, food miles, nutritional health and how much energy we use to prepare food."

Shoppers are already being encouraged to check labels to see where products came from, to prevent the wasteful transport of fresh produce around the planet.

Several major retailers are already recognising the issue by stocking more goods from local growers and producers.

But the Hallam research suggests much-trumpeted organic products are not necessarily the solution.

"Agricultural products are part of the global market and both organic and non-organic products may be imported," Dr Martindale explained.

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