Neil,

Nic Jones used lots of open tunings - he does for this song.

If you just want something to strum along to in normal tuning, the following should be a fair approximation:

[F] Willie sits in his [Bb] stable door
And he's [F] combing his [Bb] coal black [F] steed
And he's doubting on fair [Bb] Margaret's love
And his [F] heart [C] began to [F] bleed
"Give corn unto my [Bb] horse, mother
And [F] meat to my man [C] John
And [F] I'll away to fair [Bb] Margaret's bower
[F] Before the [Bb] night [C] comes [F] on"

It's easier with a capo at the 3rd fret, using the chords D, G and A.

Let me know if you need any more information.

Ed