Levy was concerned with the presumption in the Interpretation Act that articles that are posted are presumed to have been recived in the normal course of the post. It has overturned CSIS/48/1992 and a few other decisons along the way.
I dont think it has any effect on R(SB)8/89 because in the situation where the office is closed and mail cannot be delivered, the LA is making the post office bailees of the mail ( following Hodgson v Armstrong [1967] QB 299 and Lang v Devon General Ltd [1987] ICR 4)
Levy does not apply to items that are hand delivered or sent by fax or email. In this situation the date of delivery is the date of receipt, not the date someone picks up the fax or opens the email. See the decison of Mr Commissioner Jacobs R(DLA)3/05