Hi John
The Lichfield 10K is a road race and takes in a couple of hills, but I would not describe it as pretty Challenging Terrain.
We do have Whittington Barracks just outside Lichfield, but it is changing its role and is virtually deserted at present. There was a tough 10K race organised in January a few years ago. That was off road and a challenging course. It was over MOD property but organised locally. I think they had it for a couple of years and has not been run since.
I do not know of any other event that fits your description.
Bob