This is the contents of the book on ebay:

THE MALCOLM SARGENT CAROL BOOK
Eleven carols for unaccompanied mixed voices arranged by
MALCOLM SARGENT
Contents
   l. Earth's joy                         Mexican folk-tune
   3. Zither carol                         Czech folk-tune
   4. Lullaby                                 Korean folk-tune
   5. Nature carol                         Filipino plantation song
   6. Mary had a baby                         Negro spiritual
   7. De Virgin Mary had a baby boy         West Indian spiritual
   8. Silent night                         Franz Grüber
   9. Praise ye the Lord                 Moravian carol
10. Hawaiian lullaby
11. Cowboy carol                         Cecil Broadhurst

Oxford University Press, Music Deparment, 44 Conduit Street, London WIR ODE

It seems probable that this will be the carol found by Rahere (which is listed but unavailable). It might be worth contacting the ebay seller - maybe they can tell you the words, or at least the beginning of the carol, to check whether it is the right one or not.