Thanks Lester - those were exactly the thoughts that John was expressing yesterday. There's a tradition in some parts of America and Canada (for example) of individual dances lasting a very long time - circumstances where varying the melody is almost a must.

From personal experience (and most of the dances our band plays for have two tunes at most), it's often the case that a change of tune halfway through lifts the dance to a new level. For example, we pair "The Kentish Pilgrim" with "Morrisons", and you can visibly see the dancers spring with more gusto when "Morrisons" kicks in.

However, it's in the origins of "medley mania" (quite from JK) that I'm interested.