Thanks Quisling, I only queried it because it's rare to see more than one option per clue for the extra letter.
For example, 8a - Hounds dropping Barton’s birds (6)
There is only one letter you can eliminate to arrive at the answer and it's the same for every other clue with the exception of 18d where, to get "goes", you can have (b)eats or be(a)ts.