Urge politician to block stupid lie (5)
I believe the answer is:
impel
'urge' is the definition.
(thesaurus)
'politician to block stupid lie' is the wordplay.
'politician' becomes 'mp'.
'to block' indicates putting letters inside (block can mean to fill a hole in something).
'stupid' indicates an anagram (in a stupid order).
'lie' anagrammed gives 'iel'.
'mp' placed inside 'iel' is 'IMPEL'.
(Other definitions for impel that I've seen before include "Force to act" , "Urge forward, drive" , "Force forwards" , "Motivate" , "Force into motion" .)