Our eldest lives in a terraced weavers cottage which is well over 200 years old. It has solid stone floors, no cavity walls, just enough length outside the house (no drive of course) for a modern day Mini Cooper S to sit without encroaching on next door's space. But it is their house where they want to live and they love it.
To think you could insulate this house to an adequate level to make an ashp viable is fanciful. And as already mentioned where would it go?
And as the terraced houses are obviously close together imagine the noise of them all going at once 24/7?
Illustrates the point perfectly.
There are a million houses which are around 100 years old and could be knocked down and rebuilt but there a many more much older houses which you’d struggle to justify knocking down and rebuilding just for some insulation.
Also the government would need to look at compulsory purchase of tens of thousands of houses to do it.