Teuchters!! Thank you lessstressed, haven't heard that for ages!
Think Tearlach has a good kind of nondescript, posh, educated accent. Certainly not Scots, but then he'd never set foot here before the 45, but kind of non specific Europeanish.
This was what I was talking about - I read an interview with the actor who said a lot of discussion had gone into what his accent should be like.
Bill Paterson has given Ned the perfect educated clipped Edinburgh accent, as per the character's occupation/background. Sounds a lot like my Dad's telephone voice. 
I agree that only SH sounds authentically Highlander. There's a particular soft, breathiness to certain enunciations that only he seems to have.