thanks for your reply, Sam-you were right, with some cleaning the word 'Trivelox' is visible on some of the gear components-they work as you described. This is what i've found so far on Trivelox gears:they were manufactured in Birmingham, England and appeared on many makes of more upmarket British roadbikes, particularly tandems, in the 1930's. Apparently their was a British thing about keeping the line of the chain fixed and Trivelox, and Sturmey Archer, fall into this engineering tradition.
heres a pic of another Trivelox set up on a 1938 BSA tandem that i'm considering buying
your bike looks amazing BTW-i'm marvelling at how much work it must have taken to get it into that shape