Odd place to store cargo, putting learner in complete control (12)
I believe the answer is:
stranglehold
'complete control' is the definition.
(having a stranglehold means having total control)
'odd place to store cargo putting learner in' is the wordplay.
'odd' becomes 'strange' (I've seen this before).
'place to store cargo' becomes 'hold' (as in a ship's hold).
'putting learner' becomes 'l' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'strange'+'hold'='strangehold'
'strangehold' going around 'l' is 'STRANGLEHOLD'.
(Other definitions for stranglehold that I've seen before include "Complete control" , "tight grip!" , "Inexorable grip" , "total control" , "Star long held (anag) - complete power over a person" .)