Press: 'Politician admitted to awful lie' (5)
I believe the answer is:
impel
'press' is the definition.
(thesaurus)
'politician admitted to awful lie' is the wordplay.
'politician' becomes 'mp'.
'admitted to' is an insertion indicator.
'awful' indicates an anagram.
'lie' is an anagram of 'iel'.
'mp' inserted into 'iel' is 'IMPEL'.
(Other definitions for impel that I've seen before include "Cause to move forward" , "Force forwards" , "Urge or force to action" , "Urge or propel" , "Send or drive forward" .)