Prepare to paint very formal European (5)
I believe the answer is:
prime
'prepare to paint' is the definition.
(covering something with primer before painting it)
'very formal european' is the wordplay.
'very formal' becomes 'prim' (I've seen this before).
'european' becomes 'E' (abbreviation e.g. EU).
'prim'+'e'='PRIME'
(Other definitions for prime that I've seen before include "Capital - of first importance" , "Main - charge" , "First-rate; type of number" , "Prepare to set off" , "Prepare for use, say a pump" .)