Les,
The reason I raise the question is, that many of the funny songs that people like the Clancy's recorded in the 60s and 70's seem very tightly constructed with lots of clever word play and internal rhymes etc. and sound more like the product of a literate tradition rather than an oral tradition.

An ORAL TRADITION does not necessarily equate to SIMPLE songs/tunes. The Bardic tradition of Ireland and Scotland has NEVER been equalled. The Bards of Scotland, IReland, Wales, and other Celtic countries were among the most prized and talented people in those regions. The tradition of Bards goes back at least 1500 years.

These were the people who travelled across the breadth of the land passing on the messages of one region to another, swapping the news, etc. Their memories were highly developed and could keep thousands of songs and stories accurately for many decades. The greatest and the least of them were welcomed at anyone's hearth and table, and in particular that of the lords of the lands. Even then, the powers-that-be had need of the publicity machine. You may remember that most of the people of the time, including the nobility could not read or write. The PRIESTS as well as the BARDS were the only ones who could. However, due to the travelling needs, Bards needed to keep the information in their heads. It's hard enough travelling with your instrument(s), and clothing and what little food they might keep handy, but to include books or parchment would have been difficult.

Even then, people listening would have been attracted to clever word-play and such, as we do in the here-and-now.