This is a translation by Louis Blenkner OSB of the C4 text Te Deum laudamus by St Nicetas.
Blenkner was a scholar who published concerning the Gawain poet. I wrote a very dodgy dissertation on the same poet in the remote past, so I feel some kinship.
Here it is not a chant, but set to MONTANA by Henry Bryan Hays OSB and it is found in Hay’s book, the Swayed Pines Song Book. I can’t find it anywhere else so CWB may have found it there. There are some tricky time shifts lying in wait for the unwary.
This clip has the text, but you have to go to YouTube: