No doubt the numbers have been run. My strong impression was that if he started a new party that there would be enough core support (Momentum, the new membership of 600000 which is pro corbyn, the unions, students, urbanites, reboot the hype of the election before last) to get enough seats to become an entity that Labour would have to take notice of.

Suppose I never took into account the risk of a conservative party landslide. Not like a starmer labour landslide is going to have different policies tho.