Does one have to have an openable letter box? I have put a locking device on my letter box. A small bolt. So when the postie has been I can just lock the flap to stop the junk. I first started locking my flap at halloween to stop the kids putting rubbish in, but now I lock it up to stop the junk. Is it a legal requirement to have a letter flap?
There's no legal requirement to have a letter box and you can certainly put a lock on your letter box. A fair number of abandoned houses and shops have got boarded up letter boxes, for instance.
You might be interested to know that there used to be a company specialising in letterbox locks. The business didn't last long, which I suspect is because its concept relied on Royal Mail co-operating with the scheme (the company would give Royal Mail a key for the lock but postmen didn't have to use the keys).
And, a while ago I was contacted by someone who was planning to put a lock on his gate and to ask visitors wanting access to call a dedicated phone number. I'm not sure if he actually set up the system but the concept is very interesting.