From my father's solicitors files: Handwritten Letter from Prof.. John MacQueen, head of dept. School of Scottish Studies. 5th June 1971.   Dear Peter... My enquiries have elicited the following points:   

1. Ian Maclachlan of Benbecula claims to be the composer of the tune.

2. A Phd student here, one Angus John Macdonald of North Uist, who has made extensive recordings in N. and S. Uist & Benbecula was told that Maclachlan heard the tune played on the chanter by an old man in Glendale South Uist. A.J. Macdonald made enquiries in Glendale and vicinity and was completely unable to identify this "old man". No one could remember any old man in Glendale who played the chanter/

3. Ian Maclachlan has composed other tunes, eg the "Boys/Men of Glendale' (or some such title), and it is said that his style is recognisable in both this "boys of Glendale" and in the "Dark Island".

4. Attribution of "the Boys of Glendale" has never been questioned.

The uncertainties in all this will be clearer to you as a lawyer than to me, but this musch is obvious : -   All of Maclauchlin's (sic) tunes may be traditional tunes: he may just have a predilection for a certain category - possibly for out variants of a similar structure. Assuming that Maclauchlin heard the "Dark Island" melody from someone, he may have rearranged it to give it his own characteristic stamp. (Would that have been sufficient to give --- (?) copyright. You will recollect a Court of Session case some years back which concerned if my memory serves me right, "Westering Home". I seem to remember that this exact point came up.)    Professor MacQueen then goes on to say that they would have difficulty in becoming involved in any legal action, due to having to maintain an independent stance and also that they had to continue to make recordings in the Island area concerned.   

The whole truth is that rumour does not equate to fact, and with copyright generally whoever gets something in a fixed form is usually the owner of that copyright. By the same token my father Stewart Ross's lyrics to the "Dark Island" tune variant were copyrighted and fixed in sheet music as well as a recording.