A demand for the expenses, together with interest in accordance with paragraph 4, shall be served on the person from whom the authority seek to recover them.

On the date on which the demand is served, the authority shall serve a copy of it on every other person who, to the knowledge of the authority, is an owner, lessee or mortgagee of the premises.

The demand becomes operative, if no appeal is brought, on the expiry of 21 days from the date of service of the demand and is final and conclusive as to matters which could have been raised on an appeal.