35. If the local returning officer receives, before the close of the poll, an envelope other than a covering envelope and finds therein any document which it would have been appropriate to send to the officer in a covering envelope, the local returning officer shall —

(a) securely seal the envelope;

(b) endorse thereon, and sign, a statement that the envelope has been sealed with the contents intact;

(c) place the closed envelope in a postal voters ballot box;

(d) thereafter treat the envelope as a covering envelope;

and any reference in this Part to a covering envelope shall be construed as including a reference to an envelope which has been dealt with by the local returning officer in accordance with this rule.