Pondering the chain drive, the question is "Why?" The possible answer is "Because it was there".
Given that the whole thing looks like a foreigner or a home build by a very skilled man, I'd hazard a guess at someone with access to lots of buckshee sprockets and chain. So a toolroom guy from Raleigh in Notts, or given the suggestion of a Birmingham connection from Tony's site, Phillips or Dawes in Brum.
My late father was a fireman in the Blitz, and worked shifts at Phillips when he was off duty; gee I hope this thing doesn't go for a song, I'll feel I've deserted The Old Man.
I'm going to put a snipe bid in and then not look until the auction ends…. SWMBO will skin me alive!
Eug