Madmeg
I'm a Catholic and when old enough we always went to Midnight Mass. One of the lads in my primary class had older brothers and the local Trades Hall (a drinking establishment with a dubious clientele) was next to the Church.
At midnight, the drinking club would empty and my friend's Catholic brothers and all their drinking pals would pile into the church and loudly sing all the hymns and carols, before wobbling unsteadily back to the club for a few more hours.
The lovely priest welcomed them thought a few old biddies tut-tutted in disgust!
Oh that sounds exactly like my early Midnight Mass memories Madmeg. The Rising Sun Pub was about five houses along from the church, closing time Christmas Eve, I reckon a fair few of their customers emptied into the church for mass. For late comers, it was standing room only.