Pressure in support of church (5)
I believe the answer is:
force
'pressure' is the definition.
('force' can be a synonym of 'pressure')
'in support of church' is the wordplay.
'in support of' becomes 'for' (I've seen this before).
'church' becomes 'ce' (abbreviation for Church of England).
'for'+'ce'='FORCE'
(Other definitions for force that I've seen before include "Muscle" , "Urge" , "Impetus" , "Dynamism" , "Power; army" .)