Race to arrest corrupt MEP at first on trial (10)
I believe the answer is:
temptation
'trial' is the definition.
(eg temptation to sin can be a spiritual trial)
'race to arrest corrupt mep at first' is the wordplay.
'race' becomes 'tt'.
'to arrest' indicates putting letters inside.
'corrupt' indicates an anagram.
'first' becomes 'ion' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mep' anagrammed gives 'emp'.
'tt' placed around 'emp' is 'tempt'.
'tempt'+'at'+'ion'='TEMPTATION'
'on' acts as a link.
(Other definitions for temptation that I've seen before include "Enticing desire to do something" , "seduction" , "Enticement" .)