https://www.ebay.co.uk/itm/UNIQUE-CA...8AAOSwxSxdYQ4c
From the advertisement:
The frame was Worksop factory built in the 1965 -1966 era as a prototype frame, designed by Gerald O'Donovan and subsequently sold to the only previous owner, a private Carlton collector Mr M. It was chromium plated [on nickel and copper] and later finished with black / blue paintwork with early style Cobra decals. It is not a butchered / modified Cobra frame, which has different frame angle geometry.
[MENTION=191426]keidal[/MENTION] I'm very curious about how you eventually found out this amazing back story, when you started out here having little knowledge of what you had in your possession.
-Gregory