Enter intelligence agency with rum, tea (11)
I believe the answer is:
interpolate
'enter' is the definition.
(thesaurus)
'intelligence agency with rum tea' is the wordplay.
'intelligence agency' becomes 'interpol' (European police agency).
'with' means one lot of letters go next to another.
'rum' indicates anagramming the letters (rum can mean strange or unusual).
'tea' anagrammed gives 'ate'.
'interpol'+'ate'='INTERPOLATE'
(Other definitions for interpolate that I've seen before include "go-between?" , "put in the middle" , "Insert - not a reptile (anag)" , "Insert (between other terms of a series)" .)