"The possibility that MacColl's may be the "ur-text," miraculously recovered from oral tradition..."
According to Salford historians, Ruth and Eddie Frow, MacColl's father had hundreds of ballads and queer old songs, many in bits and pieces, which he sang everywhere he went - Trades Union socials, in the pub....." wherever.
MacColl was reported by the BBC man who first recruited him for the radio, to have been discovered busking for pennies from a cinema queue in Manchester , singing ballads and songs, in English and Scots Gaelic, in the hungry 1930s - long before the folk song revival was ever a twinkle in anybody's eye.

"Ewan MacColl was himself a victim of the Depression. The son of an unemployed Glasgow steelworker, who had moved to Salford in search of work during the twenties, he had suffered every privation and humiliation that poverty could contrive for him from the age of ten. His memories of his early years are still bitter—like his recollection of how to kill aimless time in a world where there was nothing else to do: "You go in the Public Library. And the old men are there standing against the pipes to get warm, all the newspaper parts are occupied, and you pick a book up. I can remember then that you got the smell of the unemployed, a kind of sour or bitter-sweet smell, mixed in with the smell of old books, dust, leather and the rest of it. So now if I pick up, say, a Dostoievsky—immediately with the first page, there's that smell of poverty in 1931."
MacColl had been out busking for pennies by the Manchester theatres and cinemas. The songs he sang were unusual, Scots songs, Gaelic songs he had learnt from his mother, border ballads and folk-songs. One night while queueing up for the three-and-sixpennies, Kenneth Adam had heard him singing outside the Manchester Paramount. He was suitably impressed. Not only did he give MacColl a handout; he also advised him to go and audi¬tion for Archie Harding at the BBC studios in Manchester's Piccadilly.
PROSPERO AND ARIEL (The rise and fall of radio, a personal recollection – D G Bridson 1971)"

MacColl certainly did learn ballads and songs from his parents - many of them he supplemented with published texts.
I would have thought that following the fiasco of attempting to attribute Irish Traveller, John Reilly's ballads as having been learned from a book, academics would have learned their lesson - apparently not.
Some of the rarest ballads imaginable have been turning up from some of the most 'unlikely' sources - Maid and the Palmer', 'Prince Robert', 'Young Hunting' 'The Suffolk Miracle', 'Johnny Scot' - all within the last 40 years.
There is no reason at all that MacColl's father should not have been such a source - I can't think of one anyway.
Jim Carroll