@Greg Hyde The mixte frames were made for decades (30s-80?; earliest were from continental Europe); they are probably making retro versions somewhere today. It looks to be mid 70s or later if the shifter is the original Sturmey-Archer. That style shifter (if I am seeing it correctly: black with black plastic trigger) was around circa 1975-76 and later; the earlier to mid 70s shifter had the black plastic trigger with a silver nameplate and Roman numerals to indicate gear selection. The 1970/71shifter was all metal except for a clear plastic cover over the nameplate.
You can also check the rear hub barrel for a date code. Sturmey-Archer had a year/month code (## ##) near the logo stamp. First 2 numbers are year, last 2 numbers are the month built (e.g. 75 11 = 1975 November); but I have a hub dated "69 13" so I can only assume it was January 1970 since there are not 13 months per year. Royal Enfield was around for decades, but became more known for motorcycles and I doubt that they made that frame. It is more than likely that the naming rights had been purchased by Raleigh/TI at that point (60s and later) and it was made by Raleigh and branded with one of their many marques that they owned at the time.
I would assume that there were fenders on it originally, and possibly a rear rack as standard equipment. Some mixte frames were built with race bike geometry; the Enfield is not one of those types (at least not for its age).