Section 7 – References to Service by Post
Interpretation Act 1978
Where an Act authorises or requires any document to be served by post (whether the expression “serve” or the expression ” give ” or ” send ” or any other expression is used) then, unless the contrary intention appears, the service is deemed to be effected by properly addressing, pre-paying and posting 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.
Practice Direction  1 All ER 889 states that, unless the contrary is proved, First class mail is deemed delivered on the second working day after posting, and Second class the fourth working day after posting. “Working Day” means Monday to Friday not including Bank Holidays.