It is a condition of the grant—
(a)that if, at any time within the initial period, the authority by whom the grant was paid serve notice on the owner of the dwelling requiring him to do so, he shall, within the period of 21 days beginning with the date on which the notice is served, furnish to the authority a certificate giving such information as the authority may reasonably require with respect to the occupation of the dwelling, and
(b)that, if required to do so by the owner of the dwelling, any tenant of the dwelling will furnish the owner with such information as he may reasonably require to enable him to furnish the certificate to the authority.