What is that gritty stuff paths at National Trust kind of places called?

[TheBunyip]

that really.

Fairly recently a path through the local nature reserve was done in that stuff. It was loose and sandy for a while and has now compacted into a pretty smooth path. I think it would be excellent for some landscaping we’re doing but I don’t have the words to google it.

Self binding gravel?

Hoggin

Hardcore

It's hoggin aka self binding gravel.

And every time I see Charlie Dimmock or those brothers use it on their gardening show I cringe thinking about how the tiny bits of grit will track through those poor peoples houses.
DM had the misfortune to have some in the garden of a house she moved to. Nightmare stuff in a residential garden with a dog!

Yep, it's muddy in winter and dusty in summer. Does stay put though.