I worked at Walls one summer, making sausages (Walls and Richmonds) and scotch eggs
The stories aren't true (lips and a******s etc

) but do yourself a favour and get them from a good butcher imo. You need meat in them, the Wall's ones are all fat and breadcrumbs.
In fact, they used to bring the blocks of fat in, and they were about the size of the yellow pages, with the thinnest sliver of red meat on them, and big thick pig hairs growing out of it. Stood on one once and my foot shout out from under me and I landed on my back