Pie and mash is a traditional London working-class food, originating from the East end of London.
Pie, mash and stewed eels shops have been in London since the 19th century, and are still common in south and east London, in many parts of Essex, and in places where there are significant expatriate British communities, including Australia where it is known as a pie floater.
During the Victorian era, due to the prevailing west to east wind, London developed in two ways: in the west and the centre, for the gentry and monified; in the east for the workers under the coal fire smoke cloud, also placing them closer to lands developed for industry and the London docks.
The working class were poor, and so looked for food stuffs which were cheap, in plentiful supply and easy to prepare. The savoury pie had long been a traditional way of preserving food, as well as in its smaller handsized form a transportable meal, protected safe from the surrounding dirt by its cold pastry crust.
European eels were one of the few forms of fish that could survive in the heavily polluted River Thames and London's other rivers at this time, and so placed in pastry crust became a common workers meal. Supply was plentiful through to the late 1800s, particularly from the Dutch fishing boats landing catches at Billingsgate Fish Market. Adding cheap mashed potatoes made it a plate-based sit-down meal, and a sauce made of the water used to cook the eels, coloured and flavoured by parsley, made the whole dish something special.
If people had a bit of money in their pocket, then later mutton or cheap mince meat with no added onion could be alternatively ordered as the pie filling.
Post World War 2, as eel supply dwindled and as beef often became cheaper, and in far greater supply overseas, minced beef became the more popular pie filling. In recent years, the popularity of eel based pies climbed again, as the propensity of people to investigate their roots and origins climbed, and the associated customs and cultures. However, since 2010, it was revealed in a joint-study by Zoological Society of London and the Environment Agency that eel numbers in the River Thames had fallen from 1,500 in 2005 to just 50 in 2010, again leading to a reduction in eel-based pie orders based on commodity price alone.