In the religious context it was very common, probably universal, in 1950's Liverpool primary & junior schools to use the terms Proddie-Dogs and Cat-olics to describe pupils in opposing schools. ...and in those days small children really did fight the other side like cat and dog.
And geographically, many Liverpool people of my generation still use the term "woollybacks" to describe the dumb yokels who have the misfortune to inhabit the hinterlands of our region. And the name "Manc" (as in 'mank') has never gone out of fashion to describe a resident of that ugly conurbation near our own glorious city.
Surely it is likely that other regions have similar derogatory descriptors for their neighbours, near and far? Wouldn't "sassenach" qualify as a 'white on white' slur?
I suspect that is because todays smug MSM and the oh-so-liberal elite like to think of themselves as 'children of the world' and above identifying with 'petty' localisms - that such descriptors are ignored by them and largely go unreported.
Those are almost cute really.
I never really heard many slurs for Catholics, guess because I'm Irish-Scots Catholic and we tend to self segregate, not so much in England, but down in the south I think class was a bigger thing when I was little.
Sassenach I definitely heard when staying with Scots relatives, but mostly just in the highlands and pretty much used on all English.
Blur nosers were more common, and that was the Scots term for protestants. I'm not sure exactly where it came from, but my family tell me it's mostly due to Rangers' strips.
I though Mancs was just a general shortening? I've always used it, I even heard people from Manchester refer to themselves by that. Self reclamation maybe?
The Oxford Cambridge battle never had nicknames from what I can remember, we just called one of our own a traitor if they went to the other. Although I do find it amusing that the dislike is still so strong there is not a straight route to go between the two.