What's the difference between a saveloy and a frankfurter?

A saveloy served with chips and curry sauce.
A
saveloy is a type of highly seasoned
sausage, usually bright red, normally boiled and often available in British
fish and chipshops, especially in
London,
Leeds,
Newcastle, and the
English Midlands and are occasionally also available fried in
batter. The word is believed to originate from the Swiss-French
cervelas or
servelat, ultimately from the Latin
cerebrus; originally a pig brain sausage particularly associated with Switzerland.
[1]
Although the saveloy was traditionally made from pork brains, the ingredients of a shop-bought sausage are typically pork (58%), water,
rusk, pork fat, potato starch, salt, emulsifiers (tetrasodium diphosphate, disodium diphosphate), white pepper, spices, dried sage (sage), preservatives (sodium nitrite, potassium nitrate), and beef collagen casing.
Frankfurter

Würstl, virsli or European vienna sausage

Smoked Vienna sausages

North American Vienna sausage in
tomato sauce
A
Vienna sausage (
German:
Wiener Würstchen, Wiener;
Viennese/
Austrian German:
Frankfurter Würstel or
Würstl;
Swiss German Wienerli;
Swabian:
Wienerle or
Saitenwurst) is a thin
parboiled sausage traditionally made of
pork and
beef in a
casing of
sheep's intestine, then given a low temperature
smoking.
[1][2] The word
Wiener means
Viennese in
German.
[3] In Austria the term "Wiener" is uncommon for this food item, which instead is usually called
Frankfurter Würstl.
[4]
So the basic difference is quality of ingredients, and edibility.