Personally, no idea... but I think I know of someone who would be able to tell you...
Faustus (Paul Sartin, Benji Kirkpatrick, Saul Rose) performed this song on their recent tour. Paul Sartin introduced it as "The New Deserter". He said that it had been popularised by Fairport/Sandy but they had reverted to what they believed was the original tune. There were some minor lyrical differences when they sang it and you can bet your bottom dollar that they would have looked in to its history and origins.
If anyone can tell you anything about Trad/Arr songs it'll be Paul Sartin. He has a page at
www.paulsartin.co.uk and Faustus have a page at
http://www.faustusband.com/.
Cheers
Nick