Nigel Parson and Geoff are referring to the unrelated children's song, "The Farmer in the dell (The Farmer Takes a Wife), which is claimed by some to be of German origin.

In abbreviated form (should be the subject of a separate thread):
The farmer in the dell
The farmer takes a wife
The farmer takes a child (nurse, cow, dog, cat, &etc. in succeeding lines.
With a "chorus" varying as to location:
Heigh-ho, the derry-o
Ee-I, tiddly-I
Ee-i, addio
Ee-i, ee-i

and even e-I-e-I-o