It was named after John Montagu, 4th Earl of Sandwich, who once spent 24 hours at the gaming table with no refreshment other than slices of cold roast beef placed between slices of toast.
The British public consumes 200 million shop-bought and home-made sandwiches every week.
M & S is the biggest seller with a turnover of about a million a week; in all, 13 million sandwiches (worth pounds 1.3bn a year) are sold each week.
The high street sandwich outlets change the size of their orders from suppliers according to the weather forecast for the following day.
A new sandwich destined for Boots' shelves will have its own 30-page specification laying down the amount of mayonnaise, thickness of cucumber slices and weight of cheese to be used.
One London sandwich chain uses 600 litres of mayonnaise every week.
An American sandwich company launched a venture to introduce the sandwich to Japan just last year.
Boots has spotted regional preferences: Londoners will go for exotic fillings - such as duck or smoked salmon - but sandwich fanciers in provincial cities stick with bacon, lettuce and tomato.
On 25 November 1986 in Staffordshire, Reg Morris ate 40 jam butties in 17 minutes and 20 seconds, each 6ins long, 4ins wide and half an inch high.