looking at its parts i would say later 70's poss 75- ive had a couple of old BSA's and falcons with similar parts, has it got steel rims , it wasnt top of its line as would of been made for the mad 70's 10speed scene
the brake levers and wheels seat post and chainset are lower end items, it would make a nice fixed gear though
if its pretty cheap i would got for it but i wouyld not pay much more than £40-50