Here at Strathaven, we are 847ft above sea level.
It is not unheard of to be able to fly microlights when the pressure is low enough that you cannot set QFE. I have seen some fantastic low pressure flying days (maybe we were in the eye of the storm!)
I understand that, in the past at least, Loganair were once stuck in the Orkneys because they were unable to set QNH on their altimeters.
After a 24 hour delay, they got permission to set them 1,000ft out, and then correct once in the cruise.
For those who don't fly commercial ops, its an easy fix.