Her Indoors' YHA Songbook (1962) attributes as follows:
W. Hope-Jones. Written about 1921 for the Eton College Boy Scouts. Printed in the Hackney Scout Song Book. We are indebted to the author for correcting (1962)The inaccurate version published in previous editions.

That has to be the definitive version, I should think. Fairly close to Reiver 2's version above, but not exactly.

Busy day coming up. I'll post the version when I have a moment and let Joe decide what to do with it.