Admirable old politician dons another layer (9)
I believe the answer is:
exemplary
'admirable' is the definition.
(thesaurus)
'old politician dons another layer' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'politician' becomes 'MP' (Member of Parliament).
'dons' is an insertion indicator (don means to wear or put on).
'another' is an anagram indicator.
'layer' with letters rearranged gives 'elary'.
'mp' put within 'elary' is 'emplary'.
'ex'+'emplary'='EXEMPLARY'
(Other definitions for exemplary that I've seen before include "Worthy of imitation" , "Worth following as an example" , "Ideal" , "Perfect" , "Outstandingly good, others should imitate" .)