Politician offering terms ripe for negotiation, including car (5,8)
I believe the answer is:
prime minister
'politician' is the definition.
(a prime minister is the head of a government)
'terms ripe for negotiation including car' is the wordplay.
'for negotiation' indicates anagramming the letters (a new arrangement of letters is negotiated).
'including' indicates putting letters inside.
'car' becomes 'mini' (Mini Cooper).
'terms'+'ripe'='termsripe'
'termsripe' anagrammed gives 'primester'.
'primester' enclosing 'mini' is 'PRIME MINISTER'.
'offering' is the link.
(Other definitions for prime minister that I've seen before include "Head of state" , "Law once in UK" , "Senior political post" , "May" , "First Lord of the Treasury" .)