Father Jack. Not Jack

In Father Ted, why does Ted call Jack 'Father Jack' or 'Father'; rather than 'Jack'?

You as a Catholic don't know the answer?

Probably respect, as he's older. It also shows, I think, that Ted and Jack aren't as close as Ted and Dougal (what with Jack being so paralytic all the time).

I thought respect as well and I've heard many a catholic priest refer to other priests as Father like it's the formal way to speak. It also helps get more laughs as we are constantly being reminded Jack is a priest and how his decadent ways contrast with the clergy lifestyle.