Police to arrest a trainee English stockholder? (4,4)

'stockholder?' is the definition.
(a meaty stock cube)

'police to arrest a trainee english' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
'police' could be 'met' (London Metropolitan Police) and 'met' is found within the remaining letters.
'trainee' could be 'cub' (I've seen this in other clues) and 'cub' is located in the answer.
'english' could be 'e' (abbreviation) and 'e' is present in the answer.
No letters remain.
This explanation may well be incorrect...