its their version if irish stew,or coddle.
another way to look at it was in years gone by,then whatever you didnt use,or binned during the week,it was lumped together and stewed to death on the day before payday as they had no dosh left to buy food with which is similar to elsewhere hence stew,or mince and tatties is just cheapo food for the working class masses.
if you look at proper souse,its just the same as the irish version.
kinda like camion stew,the difference being that in liverpool,whey you ate scouse,it was because you had nicked it from someone else. 