I would be happy to receive letters 3 days a week (in practice, that has been the case for the past 6 months even though I should be receiving letters/small parcels most days every week), but the law needs to be changed so that it isn't assumed a letter has been delivered two days after sending by 1st class with proof of postage.
Section 7 Interpretations Act 1978
References to service by post.
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.
Interestingly, "ordinary course of post" doesn't actually have a statutory definition. The two days is something of a myth that has "kind of" been viewed as reasonable in most legal settings, developed through case law precedent.
However...
Removing regular daily letter deliveries has all sort of other legislative consequences, mainly concerning road traffic enforcement, including private parking, but also things like Penalty Fare appeals, for the (very) rare person who elects to appeal by post rather than electronically.
There's probably a whole raft of other ancient statutes or practice directions that need abolishing, simplifying or replacing too concerning service by post.
There's not sufficient time in this Parliament to have such a review and get the legislation changed and implemented - so I doubt regular letter deliveries are going any time soon.