I originally asked this on the Stack GIS - incorrectly
I'm trying to get a list of special (those receive an exceptionally large amount of mail) and non-geographic postcodes (eg PO boxes).
The ONS postcode lookup provides a lookup against Grid Ref positional quality indicator but this isn't definitive. eg PO Boxes are assigned an
osind of 6 but so are other things. So this doesn't work for me.
Other than this Wiki article I can't find anything.