I am not convinced that Labour has ever lost any votes at all because of immigration.
The UKIP voters in Labour seats used to vote Tory. UKIP has never taken a seat from Labour. And now, it never will.
The very heavily public school tabloid press has projected all sorts of prejudices onto "the white working class", while in turn defining it as "traditional Labour voters".
But, at least by that definition, that projection is not borne out by the slightest electoral evidence.