In irishenglish's defense, Donegan did record Rock Island Line in 1954.    July 13, to be exact. It didn't enter the charts until about a year and a half later, but someone with Peggy Seeger's interests would probably have heard it before it became a hit.

So his point would be valid, except for one detail: Peggy didn't move to Britain until 1959. Before that, she spent much of the previous 5 years, first in Holland, then traveling and touring all over the world, including China and Russia. She wouldn't have been likely to hear Lonnie Donegan there!

Given that she was only guessing it was "1960 or so," what she really was saying, I think, was "quite soon after I moved to England."

Peggy occasionally visits Mudcat, I think, so maybe she'll pop by and set us straight. (But I think she's probably too polite to reveal the name of the cockney Lead Belly!)

PS, I guess I just snagged the pedant's crown...