18 Greens,
"ready for solo in the a/c but has let the sep lapse(test planned for next week). The weather, moon phases and student readiness were all there but the conumdrum of the lapsed sep put us off."
I'd have sent him! A pilot with a lapsed PPL but a curent medical can be sent solo under an FI's supervision just like a student, as you can see from my post above I rekon it can even be done from a non-licensed aerodrome!
Happy landings
3 point