Have just come across this thread TEN YEARS LATER, having heard "Sea Coal" performed by two ladies singing in wonderful harmony at Bracknell Folk Club this week!

Jon Boden has now also recorded a version which is widely diffused on the net (largely due to his "Folk Song a Day" project), but the tune is slightly different.

The Wilson family's version can be found on Youtube.

Thanks to George for the original post, as it includes a (first) verse which I haven't come across anywhere else. Will add it to my lyrics and try to learn it!