The truth, unpalatable to some but which is surely obvious, is that Labour is in the midst of a longstanding and possibly terminal malaise, and now finds itself facing two equally unviable options.
On one side is the current leader and a small band of leftist diehards, backed by an energetic, well-drilled movement but devoid of any coherent project and out of touch with the voters who have just defied the party in their droves. On the other is a counter-revolution led by MPs who mostly failed to see this crisis coming, have very few worthwhile ideas themselves, and are a big part of the reason the Brexit revolt happened in the first place. As the activist Neal Lawson says, the choice is essentially between different captains of the Titanic, and therefore is no choice at all.
I’ve always assumed that the United States was too diverse to sustain or be sustained by a parliamentary system. The British have their monarchy and their differently conceived, inherently conservative “constitution.” Much of this current question revolves around their difficulties, in the 21st Century, finding themselves in the mirror. We experience the same problem, but in one sense are more used to it, in another have been sustained by a different solution and still may think we know who we are, even if in the current period the focus seems less steady.
Could you imagine if the US had a parliament system? Similar currents here but it looks like Hillary’s coronation is right on schedule…