Continuing where I left off to watch crap on tele (and eat):
The Grey Cock is an Irish version, as are Mrs Costello's three other ballads and it is unique.
I'm often astounded by how ready Steve and others are to attribute such wonderful songs to the educated rather than 'the folk'
The ballad reeks of folk vernacular - 'the burning Thames' being typical, in line with the popular 'hot as the hobs of hell' folk saying and a superb example of the folk belief of the pain experienced by the dead in crossing water, the motif of many Irish folk tales
It also has similarities to the bothy night visiting song, 'I'm a Rover'
The Costello family came from County Galway, an area noted for Travellers - which means they were almost certainly familiar with Traveller songs and storytelling
In North Clare, the neighbouring county, Prof. James Delargy took stories from Paddy Sherlock, Traveller storyteller whose tales had similar motifs
Not too far from Ballinasloe, in Cloonfad., we were lucky enough to meet and take stories from one of the last of the Irish 'big storytellers' Jack Flannery
We got hour-plus long stories from him, 'The Spirit Horse under the Bridge', ' John, the Prince of Galway', 'The Cloak of Darkness' (invisibility)... and half a dozen others, all full as such motifs as are to be found in 'The Grey Cock'
Jack was a ex farmer, road worker living in a labourers cottage a mile outside Cloonfad, -
Born the week the Titanic sank, he was a masterful storyteller at 'high-art level, with all the techniques of the best of them - and a preference for "the long ones"   
Before you attribute these songs to 'the educated' you really need to be sure of your facts Steve
Jim