Get rid of English and gunners lay down the law heartlessly (9)
I believe the answer is:
eradicate
'get rid of' is the definition.
(I've seen this before)
'english and gunners lay down the law heartlessly' is the wordplay.
'english' becomes 'e' (abbreviation).
'and' is a charade indicator (letters next to each other).
'gunners' becomes 'RA' (Royal Artillery).
'lay down the law' becomes 'dictate' (to lay down the law is to dictate rules).
'heartlessly' says to hollow out the word (remove centre letters).
'dictate' with its centre taken out is 'dicate'.
'e'+'ra'+'dicate'='ERADICATE'
(Other definitions for eradicate that I've seen before include "Exterminate, extinguish" , "Get rid of, remove all traces" , "Destroy completely" , "Extinguish, wipe out" , "carry out a purge" .)