Many thanks Brendan
I have more or less finished before coming back. It was easier than I thought, but I couldn't get all the parsing, so your explanations were very helpful.
18ac I still can't tell which of my two words that begin and end with the same letters that each mean the two words in the answer. Which vowel do I use? I'm going for "e".
14d I got the answer, but couldn't parse it. I'd gone for "s" as the issue. Silly me.
I got 12ac and the use of the word overture. Thanks Jazzgirl
31ac I'd never have got that parsing without your help - so thank you
1d I got from the definition. I should have known the numbers, but it is along time since my maths "A" level.
I've just seen 9ac. I couldn't see the definition. Tricky.
10ac I can't see where the last two letters of the answer come from in the word play.
27ac I'm happy with my answer, but can't parse the last four letters.
2d I have a food stuff, but can't see the sailor.
So, what theme? Maths or something else?