Got there in the end. Made hard work of the end game by assuming that the 5 thematic elements would associate with the five triplets in a similar way. Found three and then got stuck. As a result I have spent quite a bit of time with Google learning more about the theme than was strictly required to complete the puzzle - so a win I guess.
It’s never safe to make assumptions with The Listener.
I have a a phrase from the correct and omitted letters which does not really work to indicate what to highlight, though I think I have highlighted the correct cells. My phrase is 6 4 4 6 with the sum of the first letters being 52. Is that correct?