"Is there any possible way I could lay hold of "The Song Carriers"?"
David - 'The Song Carriers' is available for downloading on this forum - CJS has been good enough to put it up
If you have trouble, P.M, me
"how the tradition was 'declining'"
MacColl's discussion of Charlie Scamp's singing was in the section on decoration - his point was how elements from other styles of singing were impinging on what he argued was "the clean, traditional sound"
It was a valid point, though I'm not sure I would have had the bottle to deal with it the way he did.
In fairness, the singer was unnamed in the programme and Charlie would have been virtually unknown to most of us at the time - he certainly was to me.
This is the section in full in which the comments were made.
Jim Carroll

"Occasionally a singer will feel called upon to emphasize or exaggerate the natural curve of a melodic line by making the voice glide gradually from one tone to the next through all the intermediate pitches. Portamento, the Italians called it and, used properly it can be an effective form of ornamentation. Jessie Murray of Buckie, Aberdeenshire, uses it with considerable skill when she sings "The Boatie Rows".

(Archives 21531, "The Boatie Rows," 1:28)

There the shallow scooping effect of the vocal line really suits the song. Portamento, however can become a very bad habit and can easily reduce a tune, rob it of its character, iron out those features which make it unique. Here is a verse of "Blackwater Side" sung by a Belfast travelling woman.

(Archives 18551, "Blackwaterside" 1 verse 1:03)

There the scooping and the sliding of the voice tend to obscure the traditional character of the song and ,were it not for the beautiful hard tone of the voice, we might well imagine that we were listening to a very mannered bar-room performer. The following singer has a large repertoire of traditional songs and ballads, all learned in the traditional way - from his parents and members of his family circle. Traditional style, however, is completely absent from his singing. The tone of voice with its vibrato is descended from classical singing; the phrasing with the unnatural pauses between naturally-joined syllables is from music-hall; the gulping of the mordents and their transformation into sobs is from crooning and the Portamento underlines as it were the complete rejection of traditional style and decoration.

(Archives 19964, "Young Leonard", 1 verse: 40)"