Labour’s forced here to trail behind grand upper class (5)
I believe the answer is:
gulag
'labour's forced here' is the definition.
(forced labour camp)
'trail behind grand upper class' is the wordplay.
'trail' becomes 'lag' (both can mean to go behind).
'behind' means one lot of letters go next to another.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'upper class' becomes 'u'.
'g'+'u'='gu'
'lag' put after 'gu' is 'GULAG'.
'to' acts as a link.
(Other definitions for gulag that I've seen before include "Soviet camps for dissidents" , "in restraint here?" , "Harsh labour camp" , "Labour camp for political prisoners" , "Labour camp in the Soviet Union" .)