Well, I was brought up calling it a Great British Butty but there are several other names for it.
Maybe I would actually call it a Sarnie more often and, of course, it would just be a Butty. Nothing wrong with embellishing the name a little though.
What Names are Used?
This the common name that is widely understood. According to Wikipedia:
The sandwich is considered to be the namesake of John Montagu, 4th Earl of Sandwich, because of the claim that he was the eponymous inventor of this food combination.
So there you have the origin of the name but what about other names?
Exactly the same but a common word in the North of England.
Also just another word for sandwich that is common in the north of England.
Now you are talking a real sandwich with a doorstop. Made from thick pieces of bread sliced from a loaf then filled. It gets the name because the end result is between 2 and 3 inches thick. In other word, enough to hold a door open.
Strictly speaking this is a bread roll rather than a sandwich. Typically a soft white, flat and round roll that is about 6inches in diameter. Then filled exactly as a sandwich would be.
At its simplest, a toasted sandwich but it gets more complicated. A toastie can be prepared by simply toasting the bread on both sides then filling. The bread can be toasted on one side before filling or it can be filled and then toasted. Then there are the toasting machines that produce yet a further result.
Have I missed any?
I am sure that there are many other regional names for what is basically a sandwich. Feel free to add the name that you use in your own area to the comments.