Every way to penetrate politician's falsehood (4,5)
I believe the answer is:
tall story
'falsehood' is the definition.
(thesaurus)
'every way to penetrate politician's' is the wordplay.
'every' becomes 'all' (similar in meaning).
'way' becomes 'st' (abbreviation for street).
'to penetrate' is an insertion indicator.
'politician' becomes 'tory' (term for a Conservative Party politician).
'all'+'st'='allst'
'allst' put into 'tory' is 'TALL STORY'.
(Other definitions for tall story that I've seen before include "Exaggerated and incredible yarn" , "guff - with 24d" , "Fairy tale" , "romance?" , "Fiction" .)