recommended mileage for run flats (when flat) is approx 50 miles (depending on manufacturer)
I estimate I have done approx 500 miles since I noticed a change
That being said, since sorting it out, I have taken off the wheel and inspected - I cant see any damage to the tyre or alloy.
However, don't like run flats as there is no warning they have gone - I'm going to change both rears ASAP