I believe his notion of "forced multiculturalism" is the 1964 Civil Rights Act, those laws that effectively eliminated Jim Crow racial segregation and discrimination in the American South. He especially opposes laws that prevent businesses serving the public from discriminating. Those were also the type of laws opposed by Enoch Powell in his famous "River of Blood" speech when he claimed such laws would inevitably lead to violence. Whether that was a promise, threat or prophecy is a matter of opinion. Although England suffers from the existence of nationalist bigots and some racist violence, the streets aren't really filled with blood and from what I saw in my last visit, the diverse people of England generally get along just fine, just as we usually do in the USA.