Are there numbers showing people being drawn to him specifically instead of the party? Again, argument isn't his policies, it's more "Isn't there a socialist candidate who people like more than Corbyn?"
I totally understand the issue they're facing internally (the ex-UKIP vote increase seems similar to the US w/ areas that love social benefits but also love denying them to other people) and why that had a role to play, as well as the "sunbelt"-esque heavily Remain middle/upper-class areas flipping to Labour. (This is different than in the US, where we're seeing the gains pretty much only on the latter side.) They made gains on both ends while losing Scotland, which is likely to have very different results in a future election because of all the weird one-off issues there. If/when Labour actually takes power, this is probably going to result in some internal strife, though again - the platform is really boilerplate. It does seem like getting some sort of Brexit compromise worked out w/ the Tories would be to their advantage, if only because that's a hot potato they probably don't want to be taking on their own, due to the fact that both parties appear to have internal fractures on the subject.