Oh Gary, Greystoke sounds like a poor old soul. Maybe you can see if you can get a trap to get him, as he sounds like he is in urgent need of a vet.
Thank you for caring and loving these precious cats.

Prayers on the way that you are able to trap him and get him the help that he needs. Even if he has to be PTS, it would be a blessing, as I am sure he is suffering in some way from the way you describe him. Poor sweet kitty.
My heart breaks for him. It's cats like this that I just want to hold tenderly and let them know that someone does love and care for them.