Thank you gem94. I'm sure I have the correct entry for 36D ( not that impressive as there are no unchecked letters ) and it checks out with Chambers OK .
I simply turned a word meaning "expression of disapproval" upside down and removed a letter (which happily was the one I was hoping for) to give a suitable entry . I can see how it could be expanded into a Group C type answer, but then I would have expected the "omission" to be the other way around to be consistent with the treatment of the other three Group C words. Maybe that isn't strictly necessary?
Anyway, I only have three clues to solve now, so I hope it will all become obvious very soon. Cheers.