Warm haddock starter for old PM (5)
I believe the answer is:
heath
'old pm' is the definition.
(prime minister Edward Heath)
'warm haddock starter' is the wordplay.
'warm' becomes 'heat'.
'starter' suggests taking the first letters.
The first letter of 'haddock' is 'h'.
'heat'+'h'='HEATH'
'for' is the link.
(Other definitions for heath that I've seen before include "Tract of open land" , "PM 1970-74" , "Barren open country" , "Scrub" , "Sandy, scrubby land" .)