Naturally I looked it up on the interwebby and as I learned of the correct spelling Gaudete (should've known that) I also remember it was made famous by Steeleye Span in the 70s, who sang it on TOTP once. Wikipedia also further informs that it's a Latin Christmas carol, from the 16th Century.
Maybe I was a monk back then and I was taken back to a previous life in my dream. or maybe it was my current fixation with 70s music which brought out the "Span" version from 1973.
Fact: the Steeleye Span single is one of only three top 50 British hits to be sung in Latin - can you name the other two?
Anyway, fingers on ears chaps and let's have a sing-along....we'll be perfect by Christmas.