Former lover criticises this writer over new increase in size (9)
I believe the answer is:
expansion
'increase in size' is the definition.
'former lover criticises this writer over new' is the wordplay.
'former lover' becomes 'ex'.
'criticises' becomes 'pans' (I've seen this before).
'this writer' becomes 'I' (the person who is writing these clues).
'over new' becomes 'on' (this might be a standard abbreviation which I don't know about).
'ex'+'pans'+'i'+'on'='EXPANSION'
Can you help me to learn more?
(Other definitions for expansion that I've seen before include "Increase in volume" , "increase in capacity" , "fatter" , "Process of increasing in size, volume etc" , "Enlargement" .)