What gets me is that the council want to paint over the graffiti with stone paint!!! ...

Precisely!

Technically, it's probably an offence to do that.
It CAN be removed, presumably (per Rollrights etc) but of course that costs a lot.
Reading the account, they seem a bit half-soaked about it - "it's not usually too bad up there" etc as if this is a general ongoing management thing, like graffitti in a park.

Looks like the Heritage Action Head of Graffitti will have to email them.
Goff?