Sod is an active legal practitioner!
Looks like a BTH KC2 manual end housing to me.
The camring looks like a twin anyway - although it is pretty manky. Same housing on KC1 with single lobe cam. With the advance and retard on the left, it would provide slack cable advance on an anti-clockwise drive mag. The contact breaker end cover was a plate secured by the three screws that aren't equidistantly spaced. Cut-out by a springy strip kissing the head of the cb centre screw.
Not interchangeable with Lucas though, or not easily. But there will be someone who needs a manual one, so worth trying to sell it on I'd say.