4N.I.An agreement between the competent landlord and the tenant made for the purposes of Part I in a case where—
(a)the competent landlord is himself a tenant; and
(b)the agreement would apart from this paragraph operate as respects any period after the coming to an end of the estate of the competent landlord;
shall not have effect unless every superior landlord who will be the immediate landlord of the tenant during any part of that period is a party to the agreement.