Castlerigg is within night-time walking distance of a campsite:
http://www.castleriggfarm.com/
Not sure if it's within your driving distance. Fairly minimal light pollution though, so might be worth a thought.
If you want any advice about which 1 or 2 berth tent to think about Harve, gis a shout, I've just done a stupidly detailed amount of research into what's out there at the minute.