Packed up when checked out for break-in (5)
I believe the answer is:
cased
'packed up' is the definition.
'cased' can be an answer for 'packed' (casing is a kind of packing). I'm not certain of the 'up' bit.
'when checked out for break-in' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'checked out for break' becomes 'ced' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'as' going into 'ced' is 'CASED'.
Can you help me to learn more?
(Other definitions for cased that I've seen before include "Carefully inspected (for crime)" , "Reconnoitred (sl.)" , "Covered, protected; checked over (by robber)" , "put in a box" , "examined with intention to rob" .)