When I took on my allotment 3 years ago last October, I discovered a fox's den in the far corner. I left it undisturbed as long as possible, but having put my adjacent greenhouse up 12 months ago, they disappeared, and I needed to clear out the far corner as it was heavily laced with rubbish and brambles. Only half of the heap has been cleared so far, and looking at continuing, I have noticed paw prints and scratchings at the entrance to the den, so I presume it is still in use. I will have to proceed with caution, as I don't really want to disturb the foxes more than possible.
I am surprised that the foxes set up a den so close to where humans are coming and going Derek. They must be very trusting. :-/
You'll have to try and get some photographs for us to see Derek. They'll keep the mice and rats away from your lottie which can only be a bonus. ;D
The den was there when I took the plot on, it hadn't been used for ten years (that side anyway) so I guess the foxes moved in during that time.
I have seen the parents and cubs on occasion, the parents seem accustomed to the presence of people.
I knew I wasn't alone today on site. Stopped to take a breather, and who was watching me on the next plot, a rather bedraggled fox. Haven't seen one in daylight round here for yonks! Very skinny and his poor tail was a sorry site. We stood and watched each other for a bit, then I got on with my digging and he/she went on his/her merry way. :)