Irregular activity from sex workers on suitable beaches (4,3,6)
I believe the answer is:
fits and starts
'irregular activity' is the definition.
(as in doing something in fits and starts)
'sex workers on suitable beaches' is the wordplay.
'sex workers' becomes 'tarts' (slang term).
'on' says to put letters next to each other.
'suitable' becomes 'fit' (similar in meaning).
'beaches' becomes 'sands' (I've seen this before).
'fit'+'sands'='fitsands'
'tarts' after 'fitsands' is 'FITS AND STARTS'.
'from' is the link.
(Other definitions for fits and starts that I've seen before include "Repeated bursts of activity" , "Irregular bursts of activity" , "Spasmodic spells" .)