A quick foray on Anc**try has revealed where-he-got-the-brass and the source of the name Bute terrace:
John Jagger m'd Annie Marshall. Her father Soloman was stone merchant, formerly a quarry labourer, started to 'do well' sometime from 1881-1891. I think we can deduce that the Marshall father-in-law helped JJ go into the building business, from being a joiner, sometime early 1900's. Hence the houses in Mona St/Bute Ter.
The name Bute terr and the Marshall residence in Brighouse - Oban house- owe their Scottish names to Soloman's wife Sarah who was b. Scotland/ Glasgow/ Kilmarnoch. Maybe Mona also has a Celtic link.