Mr. Newton and I interrupting clergyman (8)
I believe the answer is:
'clergyman' is the definition.
(minister is a kind of clergyman)
'mr newton and i interrupting' is the wordplay.
'mr' becomes 'mister' (synonyms).
'newton' becomes 'N' (synonyms).
'and' says to put letters next to each other.
'interrupting' means one lot of letters goes inside another.
'n' put after 'i' is 'in'.
'mister' going around 'in' is 'MINISTER'.
(Other definitions for minister that I've seen before include "Tend", "Member of parliament", "Merit sin (anag.)", "Member of government or clergy", "One of the clergy".)