I'd also call Argos a boutique builder. I saw them commonly the two years I worked in London and they were all fantastic quality. One look at the seat cluster here tells the tale.
Also agree they are much better known for the painting side of the house. Even in '94/'95 it seemed like local bike publications (Cycling Plus, Cycling Weekly) that they were the go-to guys in the UK for refinishing.
You've got an exquisite earlier model. Lucky!
DD