"The pros and cons of song introductions have been debated here recently"
The question of introductions to songs was a constant theme throughout the time I knew MacColl.
He thought they were essential to prevent evenings from being conveyor belt productions of songs - "next - next - next" - on the other hand, he argued that they should never be too long, nor should they be superfluous - an example was the tendency of some singers to tell the story of the song, then repeat the exercise by singing it.
He limited, (or claimed to limit) his introductions to no more than (I think - have to check) a minute and a half.
I've just been listening to an evenings of ballads at the Singers, where some of the introductions were of the best I've heard - for instance, he introduced The Keach in the Creel, with the fableaux of the renaissance painter's apprentice who fancies his master's daughter and creates a diversion to keep the parents away while he has his wicked way (said to be one of the fore-runners of the ballad) - masterful.
Occasionally he would use the introduction to place a ballad in its historical setting, like The Battle of Harlaw or The Laird of Warriston.
At other times both he and Peggy would link a song and a story, making the latter an introduction to the former.
Introductions in the sessions over here in Ireland are extremely rare, and personally, I miss them very much; I feel you can loose a lot of the song without them.
I found it rather refreshing recently when I attended an afternoon concert of ballads set up by The National Library as part of their 'Man, Womam and Child' project, to hear singers introducing their songs - it added so much to the proceedings.
I think the rule of thumb with introductions is that they should contain relevant information, be entertaining and should add something to the song rather the repeat something that's already there, though there is no harm in drawing attention to something that might be missed.
An example of this that always springs to mind from MacColl, is his savouring the beautiful description of pregnancy in the ballad, Gil Morrice when the wife confesses that Gil is her son, and not her lover, as the vengeful husband suspects "I ance was fu' o' Gil Morrice as the hip is of the stone" (stick your thumbnail into into the thin layer of flesh of a rose hip, and you'll see what I mean)
I've noticed that some of the most interested responses from audiences when we've beeing giving a talk, particularly from those who are not particularly familiar with the folk song genre, have arisen from introductions.
Jim Carroll