I'm probably never going to do it again, but just this time I'm going to side with Bo.
Buttie is a weird scouse invention, (and scouse is a weird scouse invention too), mainly created by their inability to pronounce sandwich, and it's derivatives (ie sarnie).
But there is a reason for this.
The main UK production centre for ketchup is very close to merseyside, and consequently the whole area is polluted.
Stamp out ketchup and the world can return to normality.