but do you know why there was a corresponding increase in the assets of Peel Airports Ltd in the same year
If a debt was re-assigned within the group or it's subsidiaries an impairment on one means an asset (debt due to be paid) to another, nothing fishy about that.
Its a case of dejavu with Peel and how they can run rings around local councils who own the various airports.
What is it you think they might do with all this industrial land if ops came to an end? There are umpteen vacant sites and we're hardly in a time of plenty where the land has any premium value let alone a value.