12 Prescribed procedures
1 A failure to comply with any of the requirements of regulation 11(a) or (b) above to any extent will only invalidate an application if:
(a) the applicant does not provide, when making the application, an explanation for the failure which the Secretary of State considers to be satisfactory,
(b) the Secretary of State notifies the applicant, or the person who appears to the Secretary of State to represent the applicant, of the failure within 21 days of the date on which the application is made, and
(c) the applicant does not comply with the requirements within a reasonable time, and in any event within 28 days, of being notified by the Secretary of State of the failure.
2 For the purposes of this regulation, the date on which the application is made is:
(a) in the case of an application sent by post, the date of posting, and
(b) in the case of an application submitted in person, the date on which the application is delivered to, and accepted by, a Public Enquiry Office of the Immigration and Nationality Directorate of the Home Office.