London location of a number of trees (4,4)
I believe the answer is:
nine elms
'london location' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'a number of trees' is the wordplay.
'a number' becomes 'nine' (nine is a number).
'of trees' becomes 'elms' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'nine'+'elms'='NINE ELMS'
'of' acts as a link.
Can you help me to learn more?
(Another definition for nine elms that I've seen is " part of Wandsworth - with 25d".)