Rock in Conservative charity festival (4)
I believe the answer is:
crag
'rock' is the definition.
(I know that rock can be written as crag)
'conservative charity festival' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'charity festival' becomes 'rag' (charity event at some universities).
'c'+'rag'='CRAG'
'in' is the link.
(Other definitions for crag that I've seen before include "Steep, overhanging rock" , "Steep or rugged cliff face" , "Steep rocky cliff" , "Steep rugged rock or cliff" , "Steep, rugged peak" .)