Giles,
Thanks for the pictures--this is a Falcon model that I have not seen before, although I have seen an early 80s "Ernie Clements" labeled bike with similar lug work.
I have not been able to ascertain when Falcon changed to the downtube lettering like yours (maybe someone else will chime in), with the Union Jack joining the two sides, although mid '70s seems likely. (The only catalog pages I have seen are those from the CR site, and the 1973 & 1974 catalogs that are page identical and show decals like those on the CR site from around 1970.)
Your frame also doesn't have the wrap-over stays of the earlier San Remo, or the cruder wrap-overs of the Olympic or Black Diamond. Lugs are different as well from the earlier '70s bikes.
I'm surprised too by the Cro-Moly sticker--all I have seen are Reynolds--at least main tubes, if not all 531db. That and the 27.0 seat tube makes me wonder if Falcon didn't bring this frame in from Japan...
Boy, I'd love to see catalog material from Falcon from the late '70s and '80s...
Dean Kernan
(musing in)Pomona, NY