Ernest W. wrote:
"Even if this were the case - i.e. that recreational singers in rural areas divided their songs into 'the old/orally transmitted ones' and those of more obviously recent (theatre/music hall, then gramophone/radio) provenance - clearly the majority ended up preferring the latter, or the oral tradition would not have died out."

I thought that the oral tradition died out because people simply stopped singing, not because they substituted more recent material for the older stuff. Many of the singers we know of from the 1950s and 60s had repertoires including both, but that was pretty much the last gasp of widespread recreational singing, a few surviving outposts notwithstanding.