Why did Christians in Britian BAN all Jews from entering their country for 300 YEARS ?

You asked AND answered the question? Guess nothing for us to comment on? Do you get best answer then?? LOL You can find discrimination against Jews in every country they have ever lived in for one reason, or another, as far back in history as you can reliably go. Even in Israel today some Jews are discriminated against by other Jews who don't practice the religion in the same way.