I have found it.
It is indeed by Michael Flanders.
It's in '32 Galliard Carols for Christmas' published by Stainer and Bell.
The third verse goes as follows:

If a cheese you have not got,
Then a groat must be our lot,
As we dance round the mistleto-e Buff - (Bough!) - Buff!
If you haven't got a groat,
You can go and cut your throat,
And ne'er have any Figgy Figgy,
Ne'er have any Figgy Figgy,
Ne'er have any Figgy Figgy Duff. Figgy Duff!