Consumption of sandwiches across the UK has the same environmental impact as the use of eight million cars a year.
A team from the University of Manchester arrived at the figure after studying the carbon footprint of 40 different types of sandwiches - both home-made and pre-packaged - taking account of how the ingredients were produced, the packaging, as well as food waste discarded at home and elsewhere in the supply chain.
They said 11.5 billion sandwiches are eaten each year in the UK.