TL;DR / key questions:
-Do I raise this as a grievance internally before handing in my notice? Will this achieve anything at all or just be pointless and mark my record?
-Do I have a fair case for the discrimination due to my condition being known about when I was hired? Known about by my manager.
-I am being more or less nudged off the premises by any means necessary, after 10 years here and an extended period of progressive bullying.. is there anything I can do? He gets upset and cries crocodile tears also.. which is likely why HR sided with him initially if only by appearance.
Added an edit and a few more details in some paragraphs up, does this help?