People worrying about fuel and northerly SIDs etc are all going down the wrong path here.
This crew will have had the mindset of going to EDI from the moment they entered that crew room, there is no way they planned, fuelled, set up the FMS and then briefed a flight to DUS only to then take off and fly to EDI being on a northerly SID etc. I cannot comprehend this happening.
It was likely to be a miscommunication between BACF and WDL, in that they weren't properly informed of the routes they should have been flying on the day in question.
Some airlines do not check boarding passes for a domestic flight, a possible hole in the cheese lining up.
Nor do they do a passenger announcement in a country who's language they do not comfortably speak.