So to summarise:-
Jim wrote:-
"Shirley Collins was instrumental in popularising the 'head tone' singing in the revival"

and I asked for
I'd be interested to know if Jim can
a) give a satisfactory description of that term
b) provide any evidence that Shirley set out to sing using whatever a 'head tone' is rather than singing the way that her aunt Grace, her uncle Fred or her mother or others in her family did.
c) provide any evidence that she was 'instrumental in popularising' such a style.

and Jim's responses were:-
a) 'Not sure I can' (though you were happy to use the term)
b) - not dealt with
c) - not dealt with

Now, Jim, I hope that you realise that I am not not trying to start an argument on this, I am merely trying to seek elucidation on some things that were given by you as a bald factual statements and not an opinion or a summary of studies etc. I am interested to know.

Some other points from your last post in response to my questions:-

You wrote:-
We have an example here where an excellent singer with a wonderfully rich speaking voice is on the verge of abandoning singing altogether because (thanks mainly to the fags) she can no longer handle a head tone and ends up gasping for breath at the end of lines.
So:-
* You say early in your post that you cannot give a satisfactory description of 'head tone' - yet you persist in using the term.
* You insinuate that heavy smoking cause her to lose this undefined 'head tone' gasping at the end of lines whereas the reason that she stopped singing was a traumatic incident that I don't think I should mention on a public forum - though I'm sure that Shirley would tell you if you were to ask her.
* I presume that you can substantiate your statement that Shirley is and was a heavy smoker because throughout my very long friendship with her this has not been so.

The problem for me, Jim, is that you express opinions such as Personally I find the tonal range of her singing voice far too limited to sustain my attention over a number of songs, but this is entirely down to my own tastes which nobody could possibly object to but you mix them up with statements which I feel I have to challenge. Another example - you talk about her gasping for breath at the end of lines. Can I again call for evidence or examples?