I've known the Scots term 'but and ben' since childhood, long before I heard the word 'butty' in canal terms. There is arguably some slight etymological connection conceptually. Wiki tells me:
But and ben (or butt and ben) is an architectural style for a simple building, usually applied to a residence. The etymology is from the Scots term for a two-roomed cottage.[1] The term describes a basic design of "outer room" conjoined with "inner room" as a residential building plan; the outer room, used as an antechamber or kitchen, is the but, while the inner room is the ben.[2] The word but, here, comes from Early Scots/Middle English "bouten" "outside", and ben from ES/ME "binnen", "inside".
Tam