Service engineers must cover bill for butcher (8)
I believe the answer is:
massacre
'butcher' is the definition.
(I've seen this before)
'service engineers must cover bill' is the wordplay.
'service' becomes 'mass' (kind of church service).
'engineers' becomes 're' (Royal Engineers).
'must cover' means one lot of letters goes inside another.
'bill' becomes 'ac' (short for account).
'mass'+'re'='massre'
'massre' going around 'ac' is 'MASSACRE'.
'for' acts as a link.
(Other definitions for massacre that I've seen before include "butcher" , "Slaughter, holocaust" , "Kill" , "Wanton slaughter" , "Butchery" .)