5.19.—(1) If a creditor who has valued a security subsequently realises the security (whether or not at the instance of the housing administrator)—
(a)the net amount realised must be treated in all respects (including in relation to any valuation in a proof) as an amended valuation made by the creditor; and
(b)the creditor may prove for the balance of the creditor’s debt.
(2) A creditor who voluntarily surrenders a security may prove for the whole of the creditor’s debt as if it were unsecured.