4.—(1) The costs of such investigations as may be required under regulation 3(4) shall be borne by the applicant or each applicant (in the case of a consolidated application).
(2) The Authority may, from time to time, give a written notice to the applicant or group of applicants of the estimated costs of investigation and require the applicant or group of applicants to pay such estimated costs to the Authority within such period as may be specified in the notice.
(3) At the conclusion of the investigation into the application or if the application is withdrawn, the Authority shall certify the actual costs of the investigation, and shall ––
(a)
where the actual costs of investigation are lower than the amount paid under paragraph (2), refund the excess without interest to the person who paid the estimated costs; or
(b)
where the actual costs of investigation are higher than the amount paid under paragraph (2), by a written notice, require the applicant or group of applicants to reimburse the Authority the excess within such period as may be specified in the notice.