Tombstone inscription in English mine by A.P. Herbert, originally (7)
I believe the answer is:
'tombstone inscription' is the definition.
(I've seen this before)
'english mine by a p herbert originally' is the wordplay.
'english' becomes 'e' (abbreviation).
'mine' becomes 'pit' (down the pit**).
'by' says to put letters next to each other.
'originally' indicates taking the first letters.
The first letter of 'herbert' is 'h'.
'in' acts as a link.
(Other definitions for epitaph that I've seen before include "message celebrating memories?" , "Statement of commemoration for a dead person" , "Pit heap (anag)" , "Memorial words" , "Tombstone inscription" .)