Bum gets day in lock-up (5)
I believe the answer is:
cadge
'bum' is the definition.
(both can mean to beg someone for something)
'day in lock-up' is the wordplay.
'day' becomes 'd' (abbreviation for day).
'in' is an insertion indicator.
'lock up' becomes 'cage' (I've seen this in another clue).
'd' placed into 'cage' is 'CADGE'.
'gets' acts as a link.
(Other definitions for cadge that I've seen before include "Try to borrow" , "Go about begging, scrounge" , "get free" , "Sponge (eg money)" , "Get by begging" .)