Plan second church straddling border (6)
I believe the answer is:
scheme
'plan' is the definition.
(scheming is a kind of planning)
'second church straddling border' is the wordplay.
'second' becomes 's' (common abbreviation).
'church' becomes 'ce' (abbreviation for Church of England).
'straddling' is an insertion indicator (straddle can mean to lie on both sides of).
'border' becomes 'hem' (I've seen this before).
'ce' going around 'hem' is 'cheme'.
's'+'cheme'='SCHEME'
(Other definitions for scheme that I've seen before include "Plan, ruse" , "programme" , "Lay plans" , "Program" , "'Plot, plan (6)'" .)