Sausage inna bun
The "sausage inna bun" is one of discworld's most famous foods. It is sold by Cut-Me-Own-Throat Dibbler in Sator Square or Treacle Mine Road. Once tasted never forgotten is an often used term to describe it, as, although they are quite successful they are also absolutely disgusting and may contain various products of dubious provenance.
The roundworld equivalent at least in American culture is the hotdog.
On the other hand there certainly seems to be hints of the British sausage compared to practically every other form of sausage in the world. To the uninitiated, a British sausage contains a lot of non-meat products, particularly rusk or breadcrumbs, which once upon a time were added to better stretch the meat, but has now stuck as just being the way the Brits make a sausage. The minimum meat content to be called a 'pork sausage' is 42%, which as you might imagine is shockingly low for something that is 'meat'. In cheap forms, up to half of this meager requirement is (hold on to your stomach) connective tissue. This contrasts to the many European sausages which are required to be around 90% lean pork meat. Basically, the British sausage is in theory a hideous monstrosity of what it should be, although in practice is quite tasty.