Plan for a stack in Perth to be withdrawn (7)
I believe the answer is:
formula
'plan' is the definition.
(thesaurus)
'for a stack in perth to be withdrawn' is the wordplay.
'stack in perth' becomes 'lum' (Scottish term for a chimney, eg in Perth).
'to be withdrawn' is a reversal indicator.
'a'+'lum'='alum'
'alum' written backwards gives 'mula'.
'for'+'mula'='FORMULA'
(Other definitions for formula that I've seen before include "Set expression" , "Regular approach" , "Milk substitute for babies" , "Modus operandi" , "Liquid food for infants" .)