The flavours include chicken and bacon, tuna mayonnaise, chicken tikka and cheese and onion. All of the sandwiches are on oatmeal bread, especially chosen for its ability to last for a long time, and cost £1.49.

Ray Boggiana, the food technologist who helped develop the range, said that lettuce and tomatoes has been left out as they had a tendency to go soggy. Otherwise, most of the secret to the long shelf life was down to basic food technology: removing the oxygen from the packaging and replacing it with nitrogen and carbon dioxide.

"The science is not new. It's all about using a protective atmosphere in the packaging. It's the same technology that is used in packaged sliced meats," he said, adding that sandwiches with a two-week shelf life were quite common in America.