Release Cockney dish? That gets a negative response (6)
I believe the answer is:
unknot
'release' is the definition.
(thesaurus)
'cockney dish? that gets a negative response' is the wordplay.
'cockney dish?' becomes 'unk' ('hunk' - both can mean an attractive man - said with a cockney accent, dropping the 'H').
'that gets' means one lot of letters go next to another.
'a negative response' becomes 'not'.
'unk'+'not'='UNKNOT'
(Other definitions for unknot that I've seen before include "Simplify" , "Free from ties" , "Untie" , "Remove tie" , "Loosen" .)