Dear [name of employee]
RETURN OF COMPANY PROPERTY
We are concerned that you have not yet returned [list item(s) not returned] [contrary to clause [] of your contract].
This/These item(s) remain(s) the property of the Company.
We request that you return the above item(s) to us immediately, and in any event, no later than 4pm on [date]. If you fail to return [all] the above property to us by this date, we will have no choice but to take the appropriate action on the basis that you have deliberately and unlawfully withheld the Company`s property. Such action will include reporting the matter to the Police.