Finished, after a few uses of CrosswordSolver, notably for the clever 3d when I had it as .. L.E...A, which led to completing the sparse NW corner, and a nudge which confirmed my idea for 4d.
Foi 5a
Loi 15a
Cod 3d, very clever but soundly constructed!
Haven't spent much time on it till today: away for a few days. Can thoroughly recommend the Kynren spectacular at Bishop Auckland, the main inspiration for our trip.