Very Serious People??

They hate him because he is opposed to Blairite corporatism. Which is their very reason to be in the Labour party (as opposed to the Tories, their more natural home)

keep to the Fen Causeway

Why? Because he shows up the government as grifters. He doesn't play the game, therefore they can't attack him on the usual battlefield.
So they make shit up and their buddies in the MSM throw it at the wall and try make it stick...

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty