Many thanks Zozozo
For 7d, that was the one combination of letters I hadn't tried to anagram. Doh!
I had solved 13 ac but couldn't parse it, so thanks for the explanation.
I had two possible answers for 2d, but 20ac confirmed one for me but once again I cannot parse it fully. What is the circular letter?
I have also guessed at an answer for 6d, but have no idea why it is right. I might have to think again. Is it a date?