Former PM in barren land (5)
I believe the answer is:
heath
I believe this is a double definition.
'former pm' is the first definition.
(I've seen this before)
'barren land' is the second definition.
(thesaurus)
'in' is the link.
(Other definitions for heath that I've seen before include "Open land with acid soil" , "Scrub" , "See 16" , "Sandy, scrubby land" , "Open land with scrubby vegetation" .)