27. Where any ¹[Act of Parliament] or Regulation made after the commencement of this Act authorizes or requires any document to be served by post, whether the expression "serve" or either of the expressions "give" or "send" or any other expression is used, then, unless a different intention appears, the service shall be deemed to be effected by properly addressing, pre-paying and posting by registered post, a letter containing the document, and, unless the contrary is proved, to have been effected at the time at which the letter would be delivered in the ordinary course of post.