In times past, back end of the chancel (4)
I believe the answer is:
apse
'end of the chancel' is the definition.
'apse' can be an answer for 'chancel' (thesaurus). I'm not certain of the 'end of the' bit.
'in times past back' is the wordplay.
'in' indicates the answer is hidden within the clue.
'back' says the letters should be written in reverse.
'espa' can be found hidden inside 'times past'.
'espa' reversed gives 'APSE'.
Can you help me to learn more?
(Other definitions for apse that I've seen before include "room for an altar" , "Recess at east end of church" , "Recess in church wall" , "Recess with domed rof in a church" , "Semicircular recess in church" .)