As I've said a number of times, the reason UKIP attracts people with bigoted views about race is that it has shown time and again that it does not care about putting dangerous extremists forward as candidates for office.
Every single time (and how many has it been now? Hundreds?) that a member of the party is found spouting horrible views, the response from the leadership is always the same:
"Oh... gosh, how terrible. We'll, um, we'll definitely sort it out. Yep."
Then the next one happens.
"Oh my! Again? This really is awful. Fortunately we are sorting out."
Then the next...
And this doesn't bother people. Your average UKIP supporter may well not be racist or racially prejudiced. However they are normally willing to just shrug off the above pattern - in fact rarely if ever do they see it as important. Frankly they seem eager for it to just go away.
Well, there's a reason it doesn't. A good one. Which is that it makes people who *are* racially prejudiced begin to look at the party as an appealing option. That's why Nick Griffin has encouraged people to vote UKIP, that's why it has many (most?) of the unreformed ex-BNP, that's why it has so many people with bigoted opinions.
That's why so many of them are prejudiced.