You live in the best mapped country in the world!
When I was a child in Chinnor I used to cycle along the Lower Icknield Way in summer, when the chalky clay wasn't sticky.
If I was you I would read up on old drove roads and packhorse routes; they are a fascinating part of our history and have fallen into disuse except by walkers and horse riders. They are fine for a mountain bike because the slope never exceeds what a loaded pony could manage. Every town, village and settlement was connected by a network of packhorse routes, most of which have now been relegated to footpath staus so you have no right to cycle on them.... although you may care to argue that that doesn't prohibit you from riding on them....
Old OS maps like this will give you an insight into the pre-motorised transport network of the area: