Weird. I also grew up in the UK, and I’m in my 50s now, it’s always been shoes off in my and my family’s houses. Unless it was a quick visit.
Same goes for my friend’s houses.

I’ve worked in the other people’s houses for well over 30 years in different capacities, from ‘clean’ jobs such as surveying to the more physical jobs of handyman, plastering etc. And a high percentage of the time it was shoes off as well.
Or separate clean shoes for inside.
Basically it’s easier to change my shoes than it is to clean a carpet or floor after I have trampled dirt around.

Ok, yeah, you’d get people say “don’t bother about your shoes” if I was only doing a survey, but I took them off anyways.
The only time I wouldn’t remove my shoes is if the houses were cleaner outside than inside, but that hardly ever happened.

If I had to guess I would say that in all the thousands and thousands of houses I’ve visited in the UK that 90% were shoes off.