Ailsa Craig, say, has been rented (5)
I believe the answer is:
islet
'ailsa craig say' is the definition.
I can't tell whether this definition defines the answer.
'been rented' is the wordplay.
'been' becomes 'is' (I am not sure about this - if you are sure you should believe this answer much more).
'rented' becomes 'let' (I've seen this before).
'is'+'let'='ISLET'
'has' acts as a link.
Can you help me to learn more?
(Other definitions for islet that I've seen before include "Eyot, holm, inch" , "Detached territory" , "detached territories?" , "Cay, for example" , "Detached bit of land" .)