After the Second World War, the British government invited immigration from its colonies, to solve a labour shortage and thus prop up its ailing economy. This began the first major influx of people of colour into the UK. Rather than being met with open arms, as they had a right to expect, they, and their British-born children, would often encounter horrible abuse. And still do. This must be a most alienating experience.
However, unlike in the United States, the presence of Black people on British streets was not perceived as a testament to an awful, society-wide crime, perpetrated right there on British soil by the British people themselves. It was not seen as a reproach and, crucially, white Britons did not think people of colour nursed a brooding, justified hatred against them, personally.
Modern American culture was established abruptly, by its founding generations, with an unbridgeable chasm between slavers and enslaved already in place. In contrast, British culture and society had been developing for centuries. Modern Western values had evolved from a foundation of Renaissance/ Enlightenment thought into a creed of democracy, human rights, equality and freedom, even if few citizens kept to these tenets. Modern Brits were proud of their country’s (perceived) record of diversity and inclusion. Immigrants were expected to arrive in easily-absorbable numbers, to appreciate the chance of a better life, and to integrate into British communities. They were to serve as tokenistic demonstrations of British tolerance.
However, the 1948 British Nationality Act allowed vastly larger numbers than expected to arrive in Britain. British racism was resistance to mass immigration, although the idiocies of racial theory were used to justify this resistance. It was the classic fear of foreigners with the added bonus (for the xenophobes) that foreigners of colour were instantly recognisable. The rhetoric of the British far right has always been about “coming over here and stealing our jobs, benefits, resources” and telling people of colour to “Go Home, if you feel that way”, if they complain about being ill-treated.
So, immigrants to the UK have always faced vile abuse, but of a different type, I think, to that of the United States. American racists seem to treat each ethnic minority differently, reserving their most powerful hatred for African Americans, whose anger they fear most. In contrast, British racists have traditionally made little distinction between immigrant groups, disliking all equally, as foreigners. After the 2nd World War, with Poland devastated and occupied by the murderous Stalinist Soviet Union, a small majority of respondents to a poll conducted by The Daily Mail (I think) wanted Polish refugees to be repatriated. Polish soldiers and airmen had fought with outstanding bravery in defence of Britain and British interests in the Second World War; Polish pilots had been perhaps the most effective defenders of the British population in the Battle of Britain. The Katyn Wood massacres, by the Soviets, of over 20,000 Polish officers and intellectuals, was well known. Did any of this matter to the British public? It did not. And these Polish people were white.
 They had been invited to come to the aid of the mother country, and the Empire’s only justification was that it was “the white man’s burden”: its purpose was to benefit the indigenous peoples of the colonies.
 See many sources. I just accessed “Why Did We Humiliate the Polish Aces After Their Battle of Britain Heroics?”, The Daily Mail, 29/10/2016.