Liberal reforms blocked by a Tory originally affecting both parties (9)
I believe the answer is:
bilateral
'affecting both parties' is the definition.
'liberal reforms blocked by a tory originally' is the wordplay.
'reforms' indicates an anagram.
'blocked by' is an insertion indicator (I've seen this in other clues).
'originally' suggests taking the first letters.
The initial letter of 'tory' is 't'.
'liberal' is an anagram of 'bileral'.
'a'+'t'='at'
'bileral' placed around 'at' is 'BILATERAL'.
(Other definitions for bilateral that I've seen before include "involving two sides" , "involving more than one party?" , "Two-sided" , "Undertaken by two parties" , "Involving two parties" .)