Ole i live in devon and have found some pretty demanding races through pure trail, Mud Crew and white star running to name a few. not sure how far you like to run but i have entered a 36 miler on the north Devon coastal path it has a 2500m elevation gain!
exe to axe and the grizzly are also pretty demanding races both about 1000m of climbing. I did a race on dartmoor called Dartmoor 3 in 1 which was a pretty grueling 22 miles over 3 races and about 1200m of climbing. theses arent exactly classed as 'fell' runs but i have run a few fells in cumbria and they are certainly up there when it comes to effort.