Machrihanish used to have a TACAN, there was a VOR-only civil navigation beacon nearby. Later, when the aerodrome closed, the Machrihanish TACAN was removed and the VOR became a VOR/DME using the same DME frequency as had the previous TACAN.
If someone was using Machrihanish VOR/DME ranges assuming that they were actually coming from the Machrihanish TACAN, they would not be where they thought they were.
All of which is probably irrelevant to this accident whose cause, except in the blinkered views of Wratten, Day and Hoon is still not positively determined.