Formal agreement in Conservative pamphlet (8)
I believe the answer is:
contract
'formal agreement' is the definition.
(thesaurus)
'conservative pamphlet' is the wordplay.
'conservative' becomes 'con' (abbreviation for Conservative).
'pamphlet' becomes 'tract' (synonyms).
'con'+'tract'='CONTRACT'
'in' is the link.
(Other definitions for contract that I've seen before include "Make smaller" , "Agree - get smaller" , "Pick up" , "bargain" , "four spades, perhaps" .)