Complaint of large blokes in small island (7)
I believe the answer is:
ailment
'complaint' is the definition.
(I know that complaint can be written as ailment)
'large blokes in small island' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'blokes' becomes 'men' (bloke can informally mean a man).
'in' indicates putting letters inside.
'small island' becomes 'ait' (an ait is a small island in a river).
'l'+'men'='lmen'
'lmen' inserted inside 'ait' is 'AILMENT'.
'of' acts as a link.
(Other definitions for ailment that I've seen before include "Minor illness" , "Bodily disorder or disease" , "Tummy upset, for instance" , "problem" , "Malady" .)