It's on the YouTube video #MC50 : Waterson:Carthy "Frost & Fire Live" 2006 posted by Kev Boyd in his Martin Carthy blog. The notes to the video say it's called "The Quern Song", and it's sung by The Devil's Interval with Emily Portman in lead.

I found lyrics somewhere on the net where it is called "Never Be Still (Harvest Song)", the words are attributed to Alfred Perceval Graves.

These are the actual words Emily sings:

Maids at morn, grind the good corn
Each in her mill, with a will
In go the oats, wheats and pearly barley
Down in a shower falls the flour

Winding strong, grinding all day long
Round, round and around goes the mill
Grinding turn about till the meal is out
Must never ever stand still

Those hands that are the strongest
Will find a welcome here
And they who work the longest
Shall earn the best cheer

repeat chorus