3.
—(1) The proper authority may, by letter delivered personally or sent by registered post addressed to a person who is liable for operationally ready national service at the usual or last known place of residence or business of that person, assign to that person any code or codes in words, figures or symbols and designate a mobilisation centre.
(2) The proper authority may, by letter sent in the manner set out in paragraph (1), vary or revoke any code or codes so assigned or change the mobilisation centre so designated under that paragraph.