Hi Alan, welcome to the Cabe.
It seems you've already established a lot of information re. the parts of this tandem.
As to who actually made the frame, it's very difficult to say.
As you've discovered, many small (and larger) manufacturers used 'Chater-Lea' fittings when building frames; actual 'Chater-Lea' branded bicycles are incredibly rare indeed, I know of one (solo) machine.
It's a similar scenario to most of the 'BSA' track racing bikes that are in existence, 99.99% were not made by BSA, but built from BSA fittings.
As you've also discovered, tandems are almost always owned by very enthusiastic people who are prone to upgrading them over many years of stewardship. They were often used for long distance touring, and as things wore out they would be replaced/improved when necessary.
I'm certainly no expert in these matters, but I'm not sure if this was a racing machine, certainly a high-quality machine though as the 'Chater-Lea' fittings/components suggest; although that cut-out on the chainstay could suggest a racing origin. My own 1930's 'James' Arrow Ace tandem certainly doesn't feature anything like that.
I'll share the photos, if I may, with a friend who is a very keen vintage tandem owner/rider who may have an inkling as to who might have built the frame, but as I said, it's a long shot. I'll also do some digging in the V-CC library; I'll post anything I find here later.