Where to have fun in the sun in London area, single?
I believe the answer is:
seaside
'where to have fun in the sun' is the definition.
'london area single?' is the wordplay.
'london area' becomes 'se' (abbreviation for South East).
'single?' becomes 'aside' (the A-side of a vinyl single).
'se'+'aside'='SEASIDE'
'in' is the link.
(Other definitions for seaside that I've seen before include "leisure area" , "Beach location" , "Holiday place" , "Holiday destination" , "Shoreline" .)