Euro-MP's radical leader (7)
I believe the answer is:
supremo
'leader' is the definition.
(I've seen this before)
'euro-mp's radical' is the wordplay.
'radical' indicates anagramming the letters.
'euro'+'mps'='euromps'
'euromps' is an anagram of 'SUPREMO'.
(Other definitions for supremo that I've seen before include "top boss" , "Person in overall authority" , "Big fish" , "Top dog" , "Person invested with great authority" .)