I'm with Jim on that. Darke's version is undoubtedly what you'd call a variant, if they were both folk songs. It sounds as if someone had had heard the Holst tune a couple of times thirty years ago, and tried to reconstruct it from memory. I think Darke had a bit of a nerve really, writing a "new" tune that was so like a pastiche of the original. If it works, don't mend it would have been the better principle here, leave Holst alone!