Demeter, I had the same trouble. In the end I found it listed in a Wikipedia page of names of the thematic word. Scroll down to UK, then Scottish. It's five letters long. Rather obscure, methinks.
Mt49er, I don't know whether you want help to get the answer or just to work out the addition. 'Old BT dial-up service' is a clue to the first five letters of the answer. a three-letter word needs adding to the clue after 'with' to give the last three letters of the answer, the definition being the last two words of the clue. This word is only one letter different from what has to be removed from the partner, 38d.