Labour literally has no idea who its voters are or what they want anymore. Its support base is essentially the bien pensant metropolitan middle classes, students, public sector employees and the remnants of what we used to call the working classes who vote for them out of instinct. And that's it. Almost nobody else will vote for them anymore. Their voter base is so unevenly spread across society that it's virtually impossible to devise a manifesto that's going to keep all those people happy, which means that virtually any utterance that pleases one side of the voter base will anger the other. It's doubtful whether that is sustainable in terms of keeping the party together, but it's certain that it's impossible for it to win power.
I think UKIP has served its purpose and will see its support dwindle in the years to come. The interesting question is where those votes will go. They won't go back to Labour without it changing course considerably, but a lot of them might go to the Tories if they play their cards right.
That would be an understandable feeling, but they couldn't have reckoned on Labour deciding that the best way to cure its headache was to blow its brains out. That and Brexit have offered the Tories unprecedented opportunities to steal Labour's heartlands by being seen as 'the party of real, working people' (whatever that means) and as the only party determined and capable enough to enact Brexit.
UKIP has to position itself as a worker's party on the right, a Fascist party avoiding the offending word. In that way Labour remains unelectable until/unless they ditch the loony left agenda. I fear UKIP's number may be up though. Farage is an interesting individual, Nuttall is more like a mountebank in a village fete. They have not attracted people of substance.