Given his political stance (centre - left) it would have taken someone to complain about it for it to come to the Party's attention.
Now there's two obvious types of people who would report it, either someone he's annoyed in some shape or form personally or someone from the “other side” (whatever that may be)
Now imagine the fuss that would be kicked up if the reportee from the other side saw that nothing happened after they'd reported it…
So purge or due process?
Get rid of him and it's a purge, do nothing and it’s one rule for one etc. Labour can't really win. Complaint made, due process being followed. It’s all Labour can do