English tax returns keeping about spot on (5)
I believe the answer is:
exact
'spot on' is the definition.
(I've seen this before)
'english tax returns keeping about' is the wordplay.
'english' becomes 'e' (abbreviation).
'returns' shows that the letters should be reversed in order.
'keeping' is an insertion indicator.
'about' becomes 'c' (abbreviation for 'circa'**).
'tax' written backwards gives 'xat'.
'xat' going around 'c' is 'xact'.
'e'+'xact'='EXACT'
(Other definitions for exact that I've seen before include "On the nail" , "Not approximate; inflict (revenge) on someone" , "Meticulous" , "Precise; extort" , "Precisely correct" .)