Just brilliant; that the post-war Liberal BritGov opened the doors to their Island, to all the formerly colonial wogs & Africans. Worked out swell...
It can be called “reverse colonialism”.
Race-based immigration restrictions were common before World War 2. Which meant that some nations didn't admit Jews during the 1930s. The U.S. itself had limits on south and east Europeans, with Jews often classified in the latter group.
After WW 2 there was an overreaction to Hitler's racism, a talking point that if the West ever again refused to admit anyone for reasons of race or religion, it would mean that Hitler had won.