The Labour party has an existential crisis on its hands. They were founded on the principle of protecting the labour force from the might of industrialists. They are powerless when faced with protecting workers from an over-supply of additional workers, under the simple law of supply and demand determining pay rates. (ie any influx of workers (race/nationality immaterial) with which the indigenous workers must compete makes workplace conditions tougher and hands power to the employer).
UKIP could take the populist route and claim to serve workers rights but, being generally to the right of vanilla Tories, this should be anathema to them.
Equally, a Labourite who ditched them to support UKIP has to be the kind of person who allows a single issue to overcome all their instinctive hatred of a group who are mostly ex-Tories.
All rather puzzling.