One MP’s interfering, so I’m off (7,8)
I believe the answer is:
foreign minister
'one mp's' is the definition.
'interfering so i'm off' is the wordplay.
'off' is an anagram indicator.
'interfering'+'so'+'im'='interferingsoim'
'interferingsoim' anagrammed gives 'FOREIGN MINISTER'.
(Other definitions for foreign minister that I've seen before include "Angela Merkel, for instance" , "Straw was" , "Powerful person in government" , "churchman from Rome?" , "Senior politician" .)