All the experience I have of this, albeit in private not local authority housing, is that the postman or whoever presses bells till someone grants them admission. Of course this nullifies the whole intention of security, but it is what happens in practice.

Having any form of security separate to individual property doors throws up this issue. I have recently been working on having a gate installed for extra security in an open stairwell accessing two flats. Fortunately it is easy enough to have two locking postboxes installed on the back of a gate ... a bit different if there were 10 or 20 flats. America has mailboxes outwith properties but I don't know if that would even be allowed here or even what the rules are about enabling mail to be delivered to a property. I am pretty sure for example that the Post Office would not be allowed to leave mail in internal pigeon holes even if this lay within a secured hallway or similar.

Incidentally, the reason for the gate is that nearby properties have recently been burgled. I would liked to thank the police Safer Neighbourhood team, and Jamie in particular, for coming to our property and giving very practical help in improving our security.