A stock Guardian figure? (5,9)

I believe the answer is:

store detective

I'm a little stuck... Click here to teach me more about this clue!

'a stock guardian' is the definition.
'store detective' can be an answer for 'guardian' (store detective is a kind of guardian). I'm not sure about the 'a stock' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for store detective that I've seen is " high street official".)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.