@OhDear111 the OP has had a survey. She mentioned in the opening post that she had one booked, and she's posted excerpts above. I'd responded to the OP past that point.
Regardless, my personal opinion still stands.
In my opinion, in this circumstance, I would assume that any problems would have made themselves known within 50 years. If I were buying this property from you when you came to sell, the lack of building regs would not put me off (and indeed didn't put me off my own property, where there is a second story extension, built in the 70s, with no PP, and definitely no building regs as they weren't a thing then).
I think that given you are cautious, a survey is a good thing for you, but I would also assume that they would basically slate the house because it wouldn't be up to current regulations, so instead I would try to ignore things that weren't dangerous within the report, as they are not relevant to the sale.
For me personally in that situation, I would instead take a trusted builder if I was concerned by anything specific, such as cracks, sags in the ceiling, bouncy stairs, any sign that the upstairs is really not level when downstairs seems to be, and I would try to sort out safety issues such as a handrail early after moving in.
This is what I would do and think, other posters may be more cautious than me.