See.. (neither wishing to impute bad motives to the bike shop, nor to interfere with your arrangement with five Sixteenths,) this is what I mean about bike shops. Assuming your dad bought the parts that make up that bike new in the 60s, just the frame on its own would have cost him the contemporary average weekly wage, or something close to it, and that would've been perhaps a quarter of the cost of the whole machine. The average weekly wage for 2020 was reputedly £560.
I totally agree the bike shop had little interest but i have little skill in bikes and feel it would be left to rot in my hands. Therefore offering up to a member of the forum hopefully insures that it will be looked after and may be used again. Certainly I would expect that if the bike was something really special and was worth significant monetary value, someone on the forum would point that out to me. So I came to the conclusion it's just a very nice bike that deserves to be looked after in a good home rather than left rotting in the garage.