I don't think the LE (any LE) results are too reliable a guide as to what will happen at a GE.
1. At about half the turnout of the GE only the most motivated voters turned out, most simply couldn't be bothered (especially I suspect young voters) for elections that they probably don't think mattered as much.
2. At GE's it's a lot less personal than LE's at most only the 2 leaders and maybe the odd individual like BoJo have a direct effect on the vote, with LE's the voter base is small enough for local individuals to have an effect.
I think the leader of Derby lost his seat to UKIP not because of anything to do with policies but because he is personally disliked, plenty of people hate Corbyn and plenty hate May but on a national scale these things balance out.
That said I think Labour are going to have their work seriously cut out for them to have any hope of winning a General Election.
I don't think they are going to make much if any inroad into the SNP vote in Scotland so they going to have to take enough seats off the Tories in England, It's do-able but it will need a big swing and all the polls seem to indicate there isn't one there.
We may just end up trading a minority Tory govt for a minority Labour one, but on the bright side there are more people for Labour to do a deal with than the Tories, the SNP and Plaid Cymru would deal for a price and maybe even the LibDems if they can get a little less toxic between now and then.
I also don't buy the general belief that the Tories are automatic beneficiaries of a collapse in the UKIP vote, they have a few real supporters of course but I think a lot of people treat them as a protest vote and thus there are probably a lot of people who would normally vote Labour in there as well as disgruntled Tory voters.
The UKIP are a spent force anyway now they were always a one man band, Farage may have been a cunt but he was a charismatic well-spoken cunt, kind of like an intelligent version of Trump now hes' gone, they're just coming over as sad little angry people with a chip on their shoulders.