Block that is housing politician and journalist (6)
I believe the answer is:
impede
'block' is the definition.
('impede' can be a synonym of 'block')
'that is housing politician and journalist' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'housing' is an insertion indicator.
'politician' becomes 'mp'.
'and' means one lot of letters go next to another.
'journalist' becomes 'ed' (short for editor).
'mp'+'ed'='mped'
'ie' placed around 'mped' is 'IMPEDE'.
(Other definitions for impede that I've seen before include "Delay or obstruct" , "Stand in the way of progress" , "Hinder or obstruct, say progress" , "check" , "Hold back" .)