"Phil Tanner's Henry Martin certainly has some phrases in common with Derry Down"
Not a matter of phrases Steve - much more
During the life o The Critics Group Peggy Seeger and others did a great eal on tune structures and how they fell into families
I caught th bug myself at one time but was stymied by my inability to read music, but you learned to relate tunes
Can't remember if The Deadnought ever came up, but after a simple listen to it and others it becomes obvious which belongs to what family
MacColl used the idea extensively on his own song-making - write a set of words, pick a tune, then mess abut with it.
Not bad for a bunch of 'not academics' - it's a crying shame that the work Ewan, Peggy and the Critics has become the no-go area it - very useful

To me, it's as much a waste of time being dogmatic about tunes as it is origins
If the singers didn't like the tunes when they first heard the songs they took up they either adapted them or they chose another
We recorded two brothers in North Clare with doxen or so songs between them - about six of the songs came with the same tune, and on questioning, we found they hadn't noticed

'The Coal Owner and the Pitman's Wife'.
A perfect example - another member of the family
Jim Carroll