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.

It was his use of the word declining that I objected to, when what he meant was changing in a way that does not suit my personal view. In addition what did he mean by a clean traditional sound? There are such profound regional differences in the way that decoration is handled in traditional singing and the ethnomusicologist can enumerate them, describe them, classify them - but when he starts to say that one style is right and another wrong then he is getting into dangerous territory.

.... his point was how elements from other styles of singing were impinging.....

Well, of course they were, Jim. Charlie Scamp was recorded in the 1950s. Inevitably, his singing style and repertoire were both a synthesis of the songs and style that he had sung amongst his family and friends and what he had heard on the radio and records; Frank Sinatra, Jimmy Rogers et al. I would regard both a good influences. The joy is in how he is prepared to sing the old songs in a way that seems vital and modern to him and not purposefully archaic.
As far as we know traditional singing style has never existed in a vacuum.
You have recorded hundreds of hours of traveller singers. The material and style will show varying influences from outside the tradition because the tradition does not and cannot exist with absorbing outside influences and as far as we know, it has always done so.