Charles McDevitt and Nancy Whiskey.
Their recording, Oriole CB 1352, 1957, "Freight Train," credits Cotten and McDevitt as near as I can find out from later pressings of the track. In 1957, he performed it in the States.
In view of McDevitt Skiffle approach, the joint citation seems reasonable.
Elizabeth Cotten and Sanga Music secured copyright for Freight Train in 1957, following court action. She was singing the song in 1952 according to the Traditional Ballad Index. Many covers credit her.

Frankly, how the UK handled copyright and citations by UK record companies received little attention here. I can find no verification that McDevitt and Whiskey ever claimed original copyright.