London landmark lady matriarch constructed (9,4)
I believe the answer is:
admiralty arch
'london landmark' is the definition.
(I've seen this before)
'lady matriarch constructed' is the wordplay.
'constructed' is an anagram indicator.
'lady'+'matriarch'='ladymatriarch'
'ladymatriarch' with letters rearranged gives 'ADMIRALTY ARCH'.
(Other definitions for admiralty arch that I've seen before include "London landmark between The Mall and Trafalgar Square" , "Entrance to The Mall off Trafalgar Square" , "building in London" , "Building between The Mall and Trafalgar Square" , "It stands at the Trafalgar Sq. end of the Mall" .)