It isn't coffin kicking or "digging up" a dead singer. It says in the excellent biography by Ben Harker that he was cremated. So it should be "ash agitating' or some such if an alliterative punch line is required.

Also I listened to about half of 'The Big Hewer' and did not much like it except for the bits where the miners talked. MacColl has this very odd way of improvising round melodies which might have resulted from the application of techniques devised on an analogy with movement in acting. There is bonkers banjo music all through it. If you want an effective song with the word 'down' in, I recommend Ry Cooder and friends 'Down in Mississippi'. https://www.youtube.com/watch?v=CXKQlCQKtIg

Ben Harker has some incisive comments on aspects of the lyrics to the MacColl song in an early book on pop music.

Peggy Seeger is more than just Ewan MacColl's widow, as she is unfortunately characterised above. She is in a new relationship now, and has to that extent moved on. I don't care much what she may have said at some point in the past about people criticising him after he was dead. Repeating it over and over isn't for me particularly persuasive.