Joke about uniform left in labour camp (5)
I believe the answer is:
gulag
'labour camp' is the definition.
(Soviet Union labour camp)
'joke about uniform left' is the wordplay.
'joke' becomes 'gag' (a gag is a joke or witticism).
'about' indicates putting letters inside.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'left' becomes 'L' (common abbreviation).
'u'+'l'='ul'
'gag' going around 'ul' is 'GULAG'.
'in' is the link.
(Other definitions for gulag that I've seen before include "Soviet detention camp" , "Soviet forced labour camp(s)" , "Book by Solzhenitsyn 'The . . . . . Archipelago' about detention camps in USSR" , "Labour camp in the Soviet Union" , "Place for political dissidents" .)