A very pleasant and satisfying solve, with a theme that's certainly been used before, sometimes bringing in other related material, but perhaps not as a Listener. Couldn't believe that the rapid grid-fill didn't have to be followed by tormented grid-staring. This wasn't Phi at his Kea- or Sabre-emulating fiercest, but after the last three weeks I was glad of that.
I assume that the single significant letter was just short-hand for the thematic source. Shouldn't it have been two lines lower in the grid?