>>2852146I'm planning a solo trip to Kielder soon too, as
>>2852622 said it's mostly nav that's the challenge. I've camped at the site there previously and walked the eastern route alongside the reservoir, my plan for the next trip is to get dropped off at the village, stay a night in the forest and then make my way down to Hexham.
Do post if you end up doing it, I've got some new winter gear to test out so I'm gonna do a smaller trip first before I strand myself in the forest.
Pic is from a day hike by Alston on the 20th Dec.