Late news: small crush detains head of Transport (4,5)
I believe the answer is:
stop press
'late news' is the definition.
(I've seen this before)
'small crush detains head of transport' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'crush' becomes 'oppress' (synonyms).
'detains' is an insertion indicator.
'head of' says to take the initial letters.
The initial letter of 'transport' is 't'.
's'+'oppress'='soppress'
'soppress' enclosing 't' is 'STOP-PRESS'.
(Other definitions for stop press that I've seen before include "Hold the front page!" , "newspaper feature" , "The way to be tyrannical" , "Latest news" , "breaking intelligence" .)