Rhianon you dont by any chance mean the one that uses the Volga Boatmen tune?
The way I heard it sung by assorted Mudcatters lead by Tom, Judy and Hannah Goddard at last years Getaway was
"Happy Birthday, Ug (this was more a grunt than Ug)
Happy birthday Ug
Gloom and despondancy are all around you
Happy Birthday, Ug Happy Birthday, Ug
there were acoupla other verses in the same vein
and the final verse
"Happy Birthday, Ug Happy Birthday, Ug
may the candles on your cake burn like cities in your wake
Happy Birthday, Ug Happy Birthday, Ug