The formula for the perfect SANDWICH: 'Real' butter spread right to the edges, two slices of brown bread, double folded meat and DEHYDRATED tomato

Today, millions of people will be assembling their favourite fillings between two slices of bread today in celebration of National Sandwich Day. 'Wet fillings, like slices of tomato, need to be sandwiched in middle and insulated from making the bread soggy,' said Charles Spence, professor of experimental psychology at the University of Oxford. According to scientists, the perfect sandwich has a symmetrical arrangement of fillings and between a robust bread spread with room temperature butter During construction, rather than building your sandwich from the bottom up, you should place both pieces of bread side by side and add each filling sequentially. Professor Spence says: 'The fundamental purpose of the Earl of Sandwich’s invention is to keep one’s hands clean, so that might rule out greasy breads such as focaccia.' Surely there's are few snacks that capture the nation's heart like the sandwich, which was allegedly devised by John Montagu, the 4th Earl of Sandwich, in 1762 Also, getting as wide a range of colours into a burger can 'make what we eat look more attractive', from the green of the lettuce to the red of the tomato.