1A) Cantab's current second team takes on Oxon's first - who's the winner? (3,4) C??,?O?O
12A) Class of fish in one's pond for a change (6). I can only come up with "Dipnoi" but I think that is wrong.
12D) Prolific Greek scholar undertook first year calculation in reverse (7).
At first I thought it was "Erasmus" but if "Dipnoi" is correct, then Erasmus is incorrect.
15A) Time for Christmas drink and children presenting poem (9) ??????I?H
19D) Poetry in audition is outstanding (3) O??
20A) Meteorologist's guide to damage done after onset of storm (5) S????
As always, please could you explain how you arrived/parsed the answer as I am still a novice when it comes to cryptic clues. Thanks in advance. Time for peanuts and a glass of wine now. My head hurts.