Dear Bob

You are a star and I am much indebted!
Your comments have opened up a real avenue of enquiry.
Yes - the Torn A' Ma Goon lyrics are what I was thinking of from the Pasolini "Canterbury Tales". And a bit of a 'net search I think would confirm to me that the singer was Jimmy McBeath.
That lead helped me find out a couple more answers I was seeking:
(a) the "Royal Forester" version heard in the film was that recorded by Alan Lomax as sung by John Strachan
(b) the version of the "Farmers Cursed Wife" was another from the Lomax recordings, being sung by Thomas Moran and not, as I thought, by Seamus Ennis.
(c)another song heard in the film is "The Mermaid", but situated in Fishguard Town rather than elswhere.

The other songs I recognise from the film, or don't and would like assitance are:-

"The Old Piper of Balaboreen" - possibly sung by Seamus Ennis
"The Little Journeyman" - probably sung by Sarah Makem
"See the little fishes .. how they sport and play" - definitely the Copper Family, but dunno the title
"Paddy`West's House" - sung by actor Hugh Griffith
"We were ploughing our way down the wild Irish sea" - no idea for title or singer
".son of a bitch .. that gave a poor fellow the itch" and also "where I can find her" - no idea again, sounds like a rugby song!
"Veni Sancti Spiritus" - by Archbishop Langton

Thanks again for your help!