I linked this in aNt's thread also, but it's apparently a traditional Welsh hymn called Calon Lân:
http://en.wikipedia.org/wiki/Calon_Lân
Sorry if this has come up before, but what is Underworld's connection to Wales? I mean, it comes up regularly in their work, such as this Welsh hymn, "Best Mamgu Ever", Welsh language lessons in the radio broadcast, just to name a few. Can anyone enlighten me?