Continue being eager to hold work up (4,2)
I believe the answer is:
keep on
'continue' is the definition.
(I know that continue can be written as keep on)
'eager to hold work up' is the wordplay.
'eager' becomes 'keen' (I've seen this in another clue).
'to hold' indicates putting letters inside.
'work' becomes 'op' (abbreviation for opus).
'up' is a reversal indicator (in down clue: letters go upwards).
'op' written backwards gives 'po'.
'keen' placed around 'po' is 'KEEP ON'.
'being' acts as a link.
(Other definitions for keep on that I've seen before include "Continue, persevere" , "Continue; not dismiss" , "Continue; retain in service" .)