My dad taught me that twang was a kind of slab toffee, ( Hence the Twangmans Mot' having a treacle factory for his source of sugar). You would get a square foot of it for tuppence, and if it didn't stick to the counter, you got your money back! So you needed a knife and/or hammer to break the slabs up.
He also said that ' mot ' was a shortening of Moth, as in delicate butterfly, but with a less than generous implication! Similarly, Midge was a delicate fly, flitting from place to place, like lots of young wans in those days!