Us Brits love a good sandwich but our eating habits are damaging the environment.

The overall annual consumption of sandwiches across the UK has the same impact as the use of around eight millions cars, according to scientists.

Research from the University of Manchester has tested both home-made and pre-packaged sandwiches, taking account of how the ingredients were produced, the packaging, as well as food waste discarded at home and elsewhere in the supply chain.

The team calculated the carbon dioxide equivalent of the 11.5 billion sandwiches eaten each year in the UK.

Professor Adisa Azapagic, from the university's School of Chemical Engineering and Analytical Sciences, said: "Consuming 11.5 billion sandwiches annually in the UK generates, on average, 9.5 million tonnes of CO2 eq, equivalent to the annual use of 8.6 million cars."

The ready-made 'all-day breakfast' sandwich containing egg, bacon and sausage was found to have the highest carbon footprint, generating 1,441 grams of CO2 eq - which is the same as driving a car for 12 miles.

Those containing pork meat (bacon, ham or sausages), cheese, tomato or prawns were also deemed as carbon-intensive by the researchers but homemade favourite ham and cheese was found to have the lowest CO2 eq.

Keeping sandwiches chilled in supermarkets and shops accounts for up to a quarter of their greenhouse gas emission equivalent, the researchers said, adding that making them at home using the same ingredients could reduce carbon emissions by 50 per cent.

The team concluded that a combination of changes to the recipes, packaging and waste disposal could halve the carbon footprint of the sandwiches.