There's a strange right-wing belief that the British are a pure-bred race and that foreigners are a bad thing.
From romans, through saxons, danes and vikings to the normans who gave us our feudal system. From the mix of french, spanish and dutch who were involved in the glorious revolution and rise of our current monarchy to the european refugees of the thirties and american GIs. From the hardworking asians and west indians of the seventies and eighties to the easten europeans of today.
Doesn't our mongrel history make it more difficult to think in terms of them and us?