No because "Brit" is never used as an ethnic slur.

For a good example of P* being used in a derogatory form, watch Bend it like Beckham, where it's used against an Indian girl because of the colour of her skin.

People don't push dog shit through your letter box and spray paint "pakis out" if you're white British, but they do if you're Pakistani, Indian, Bangladeshi, etc etc.

Is "Brit" widely used in a derogatory sense when bullying or attacking British-looking people? You can't decide "slur or not" just by "is it a shortened form of a country name".

Despite that you’re getting downvoted, I’m rather curious about the connotation of these words myself.

In the UK it's a derogatory catch-all term for anyone that vaguely looks South Asian and was initially widely publicized in the 60s/70s around "paki-bashing" (= aka "lets gang up and beat up some immigrants").

A few years of hearing skinhead Nazis shouting "pakis out" will do that to a culture.