Peter, sorry for the delay, I've been away from the PC for a few days.
The "Radio ballads" were produced in the late fifties early sixties by Ewan, Charles Parker of the BBC, and Peggy Seeger. They were a completely new form of story telling for radio, combining as you say, recordings of the people involved (speech and song), traditional songs and new songs in the folk idiom. From Memory there were seven in all:
The ballad of John Axon. - The story of the John Axon GC and the train crash in which he was killed.
Singing the fishing. - The story of East coast herring fishing from the 1890's to the (then) present day. This won the Italia prize for best radio program, and of course contains what is probably MacColl's second best known song "Shoals of herring"
The Travelling people - story of the life and persecution of the Romanies.
The big Hewer - about mining
The fight game - boxing

The names of the other two escape me but they were about long distance lorry drivers, and the current youth culture.
The first three listed were re-broadcast by the BBC in the early eighties, and by all accounts had as profound an effect on audiences then as they did originally. I remember hearing one teenager ask why they didn't make programs as good as that these days!!

Some at least were issued on record - Argo I believe. But I remember asking Ewan about re-issuing them and being told that whoever had the (record) rights was sitting on them and would neither re-issue nor sell the rights back to him. That was a long time ago of course, and I have no idea who currently owns the rights or what their status is. (Presumably the BBC still owns the rights to broadcast)

Best of luck in your hunt.

Pete M