Well, I carefully said that Hamish Henderson stated this tune relationship before me. I then thought about it, and considered that I could recognise a good family sequence of these song tunes. I know that others disagree. I do not have the musicologist skill to explain what I am identifying in the shape, the distinctive lift in the second half of the tunes, and the key notes in the tunes, sorry. We hear what we hear, and make sense of it as we can.
Hamish Henderson wrote to me that in 1943 he heard 'The Bloody Fields of Flanders', a pipe march that was made during the First World War, played on the beachhead at Anzio in Italy, and remembered it when he came to write the 'The Freedom Come-All-Ye', and before that for 'The John Maclean March'.
Cliff Hanley wrote his lyric 'to an old pipe tune' for a show in the Glasgow Empire music hall in around 1950, to first be sung in public by Robert Wilson, who needed a song to close the act of his performance at a Christmas Scottish review musical show. Perhaps someone more knowledgeable can identify a different pipe tune as Cliff's source?