Rabbits, crows etc. .22rimfire, .17hmr, for foxes .223 is a good all rounder, but there's also .17 & .22 hornet, .204 &.222, but the .223 is the most popular.
The gamekeeper will keep you right with these calibers, if you progress to roe deer at any point the .243 would be the one, and of course it will take care of the foxes as well.
Wish you success with your new permission, enjoy. ?