On further reflection, the theme is absolutely brilliant! The letters referred to in the clue of 13 spell out the solution of 13. 22 is not an exception. I didn't congratulate Brendan the setter enough.
Evening all (both)
Not so straightforward for me this time.
FOI was 5a, and prob COD as well.
But I think I see the theme - thanks geeker, but no ideas for on 1d
-E-N-T-I
or 15d
Any hints appreciated.....