Somebody on another forum I read claimed that the tune was used for a traditional maypole dance at Barwick-in-Elmet, which was where he was from. But he couldn't find any more about it.

Amazing video here, but no Archers theme tune:

http://www.barwickinelmethistoricalsociety.com/polecine99.html

It seems likely that such a big event would have its own special tune, but if it did the historical society hadn't found it either.