Re Labour left: look at the demographics of 2017 and 19 elections in which Labour members went up to over 500K.
In short, nearly all young voters were on board with renationalisation, wealth taxes, an end to supporting US dirty wars, ... and media reform, with the very different Labour of the time in majority right up to the 40s age bracket.

That united swell of support for such policies has been scattered, many going with Polanski's Greens.