I had heard the quote given by DaveRo above, about it Jay Ungar (not Jungar!) himself saying that he wrote it “in the style of a Scottish lament”. As a Scot, I don’t find it particularly Scottish sounding, and that one Cnat doesn’t really make it a mixolydian tune, if you compare it with our many “mix” pipe tunes.
I do think it is a lovely tune, but needs to be played slowly - yes, as a lament - with lots of expression, rather than romped through mechanically as a swingy waltz which happens in too many pub sessions.
I was somewhat gobsmacked to hear a different arrangement the other week, when it was put into an up tempo 4/4 almost reggae rhythm: almost unrecognisable: I hope Jay got his royalties for that!