They work hard on Greek desserts (8)
I believe the answer is:
grafters
'they work hard' is the definition.
(I've seen this before)
'on greek desserts' is the wordplay.
'on' means one lot of letters go next to another.
'greek' becomes 'gr'.
'desserts' becomes 'afters' (informal UK term for the course after a main meal).
'gr' put next to 'afters' is 'GRAFTERS'.
(Other definitions for grafters that I've seen before include "Hard workers" , "They work hard" .)