"as recently as 1947 in London "

So 80 years doesn't make a tradition? Look at Dickens' rendition of Cockney dialect, and compare it with early 20th century music hall's- the source of gor blimey guvnor etc. Or, apart from maybe one or two, no Derbyshire well dressings can be dated earlier that the 1880s, patronised by nice vicars. And in English folk music, the thread of continuity is very tenuous; even the musical style of today bears little resemblance with early 20th century recordings (scrapy fiddle, straight up-and-down melodeon).

I can only speak for the Irish tune tradition; the session may be "recent" but the music is flourishing - and evoilving- in a way that aspicians won't appreciate.