I'm sorry if someone has mentioned this before but surely what is being discussed here is a bacon sandwich rather than a bacon 'butty'?

Any Liverpudlian will tell you that a 'butty' is ONE slice of bread (the crust of the bread for preference) thickly buttered and finished off with dollops of jam.

The 'jam butty' of Ken Dood and the Diddymen fame, in fact.

Though I'm prepared to concede that, through custom and practice, 'bacon butty' might be considered legitimate by some, even though TWO slices of bread are involved.

Perhaps I should get out more?