Prudish cleric welcomes European head of government (5,8)
I believe the answer is:
prime minister
'head of government' is the definition.
(I've seen this before)
'prudish cleric welcomes european' is the wordplay.
'prudish' becomes 'prim' (synonyms).
'cleric' becomes 'minister' (church minister).
'welcomes' is an insertion indicator (in sense of 'invites in').
'european' becomes 'e' (abbreviation e.g. EU).
'prim'+'minister'='primminister'
'primminister' enclosing 'e' is 'PRIME MINISTER'.
(Other definitions for prime minister that I've seen before include "May" , "Senior political post" , "Government leader" , "Head of government" , "PM" .)