Wild camping is technically illegal, but tolerated in the Lake District as long as you're sensible, and discrete, about it.
Some decent pitches in the area you're interested in :
Styhead tarn - can get very busy at times though
Sprinkling tarn - quieter than Styhead, but also more exposed
Angle tarn ( Langdale ) - only a couple of pitches there, but pleasant enough
There are a few hidden pitches that are superb, but I'm not willing to share the locations