I'm not actually sure that's true. I mean, yes, Corbyn did very well among lefty-liberal young London metropolitans, but there aren't enough of them to win the Labour leadership. Corbyn absolutely dominated all the other three candidates among working class Labour voters; middle- and high-income were much more likely to plump for Burnham or Cooper. Those working class Labour voters were very likely to be Brexit.
I think the Labour party is in for a really rough time. It's going to have a proper showdown between industrial Labour and urban(e) Labour, and god knows what will still be standing afterwards.