Report returned with old reliable person (7)
I believe the answer is:
trooper
'reliable person' is the definition.
'trooper' can be an answer for 'person' (trooper is a kind of person). I'm not certain of the 'reliable' bit.
'report returned with old' is the wordplay.
'returned' says the letters should be written backwards.
'with' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'report' reversed gives 'troper'.
'troper' going around 'o' is 'TROOPER'.
Can you help me to learn more?
(Other definitions for trooper that I've seen before include "ship" , "Private soldier" , "He swears" , "Cavalry 21" , "Cavalryman" .)