Conservative policy in document is rejected (8)
I believe the answer is:
declined
'rejected' is the definition.
('decline' can be a synonym of 'reject')
'conservative policy in document' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'policy' becomes 'line' (as in the party line).
'in' means one lot of letters goes inside another.
'document' becomes 'ded' (I can't explain this - if you can you should believe this answer much more).
'c'+'line'='cline'
'cline' inserted inside 'ded' is 'DECLINED'.
'is' is the link.
Can you help me to learn more?
(Other definitions for declined that I've seen before include "Refused; waned" , "sank" , "Went through cases" , "Refused, rejected" , "Refused or became weaker" .)