Corby supports Brexit, there is a video of him saying that he doesn't want Britain to be part of a European empire.
It could be a case of the enemy of my enemy is my friend.
After all Churchill had to get pally with Stalin to defeat the greater threat of Hitler and his attempt at a European empire.
A lot of these anti Corbynites are really Blairites in disguise who would if they managed to get into power try their utmost to undermine Brexit.