Coffindodger I was stuck with 18d and 19d too. I had the answer to 18d but could not see how it was constructed, and 19d was still a complete mystery. Thanks Brendan and Mathi for enlightening us!
Another enjoyable Everyman, despite the dodgy homophone at 23a. [This might be a bit of a spoiler:] I guess in some parts of a sentence the not at all might be pronounced rather like the sister - I have been thinking up various sentences to decide whether or not this clue is fair.