Apologies if anyone else has picked this one up earlier in the thread.
Looking at 16 across I had 'swallowing drug' as extra words. The clue seemed to parse perfectly well without these words and didn't seem to parse with them. Since ACE is a drug, S and G would be extra letters. The phrase (no comeback?) needed a U and N in their place pointing me to 18 across. So what is the correct parsing of 16 across?
I've completed - which is a good result for me as I normally manage just one in five. Presumably this is an easy puzzle.
I think this thread serves a very useful purpose. My GP agrees. We were discussing it this morning when he was reviewing my dosage of an ace (or more properly an ACE) and saying that puzzles like this ward off dementia .