that "leaf" cap on the seat stays was something favored by Bernard Carre (France) but also by Jan LeGrand who was chief mechanic for Raleigh TI and probably had some influence on the SBDU frames. Besides that little bit, I have no idea about this particular frame...looks good, though. I'm sure it wouldn't have those details (under-BB cabling, braze-ons, short dropouts) if it was built in '69.
If it was a LeGrand "Presto" (his own brand) it would have other give-away details like a diamond-section brake bridge and "XXX" marking on the BB shell, etc.