Where any enactment requires, expressly or by implication, that a summons in respect of an offence shall be issued or served within a specified period after the commission of the offence, and service of the summons may under [F1rules of court] be effected by post, then, if under the rules service of the summons is not treated as proved, but it is shown that a letter containing the summons was posted at such time as to enable it to be delivered in the ordinary course of post within that period, a second summons may be issued on the same information; and the enactment shall have effect, in relation to that summons, as if the specified period were a period running from the return day of the original summons.