WHEN THE CALL COMES
I have just found a Youtube video of a song about the Spanish Civil War called "When The Call Comes" performed by George Archibald and Ian McCalman which is recorded on the Greentrax CD "Scots In The Spanish Civil War".
More on this CD Here
You can hear it with this link:

When The Call Comes by George Archibald & Ian McCalman
If anyone knows more information about the origins of this song or can give the complete lyrics then please post below