Conservative whip and senior journalist disagreed (7)
I believe the answer is:
clashed
'disagreed' is the definition.
(clashing is a kind of disagreeing)
'conservative whip and senior journalist' is the wordplay.
'conservative' becomes 'C' (abbreviation commonly used in UK politics).
'whip' becomes 'lash' (synonyms).
'and' says to put letters next to each other.
'senior journalist' becomes 'ed' (abbreviation for editor).
'c'+'lash'+'ed'='CLASHED'
(Other definitions for clashed that I've seen before include "Was incompatible" , "Came into conflict" .)