A child Marryat abandoned in London landmark (9,4)
I believe the answer is:
admiralty arch
'london landmark' is the definition.
(I've seen this before)
'a child marryat abandoned' is the wordplay.
'abandoned' indicates an anagram.
'child'+'marryat'='childmarryat'
'childmarryat' with letters rearranged gives 'dmiraltyarch'.
'a'+'dmiraltyarch'='ADMIRALTY ARCH'
'in' acts as a link.
(Other definitions for admiralty arch that I've seen before include "building in London" , "London landmark between The Mall and Trafalgar Square" , "Building between The Mall and Trafalgar Square" , "Entrance to The Mall off Trafalgar Square" , "It stands at the Trafalgar Sq. end of the Mall" .)