Bangers & Mash is a traditional British dish. Bangers are so named because sausages used to rupture (or even pop) while cooking. Mash simply refers to the mashed potatoes. Over the years, recipes for Bangers & Mash are endless.
In World War I, due to shortage of meat, butchers added minute amount of water to the case filling to increase bulk/size/weight. This made the sausage case likely to pop when cooked because the added moisture steamed into pressure.
This practice of adding water was banned by the Ministry of Food after World War I.
This dish, even when cooked at home, may be thought of as an example of pub grub — relatively quick and easy to make in large quantities.
Today up-market sausages and mashes are often served in UK public houses.