Conservative Heather to hold tight (5)
I believe the answer is:
cling
'hold tight' is the definition.
(I've seen this in another clue)
'conservative heather' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'heather' becomes 'ling' (synonyms).
'c'+'ling'='CLING'
'to' is the link.
(Other definitions for cling that I've seen before include "Hold, cleave" , "Hold tightly, become attached" , "have emotional attachment?" , "fast" , "Clasp closely" .)