5.  For the purpose of determining the duration of the periods referred to in regulation 4 above, the following rules shall apply —

(a) in the case of the period mentioned in regulation 4(a) above, it shall be taken to have begun on the date when the Commissioners first raised the inquiry and it shall be taken to have ended on the date when they received a complete answer to their inquiry;

(b) in the case of the period mentioned in regulation 4(b) above, it shall be taken to have begun on the date when the error or omission first came to the notice of the Commissioners and it shall be taken to have ended on the date when the error or omission was corrected by them;

(c) in the case of the period mentioned in regulation 4(c)(i) above, it shall be determined in accordance with a certificate of the Commissioners under paragraph 11(1)(b) of Schedule 7 to the principal Act;

(d) in the case of the period mentioned in regulation 4(c)(ii) above, it shall be taken to have begun on the date of the service of the written notice of the Commissioners which required the production of documents or the giving of security and it shall be taken to have ended on the date when they received the required documents or the required security.