Who Controls the Mailbox? Demised vs. Communal Post Boxes (and How to Fix or Replace Your Lock)

You lose your keys, or you move into a new flat and find the post box key was never handed over. You go down to the communal entrance, look at the wall of neatly stacked metal boxes, and wonder: is this one for the managing agent, or is it on me?

It is one of the most common points of confusion in leasehold blocks. Here is who owns what, how to order a replacement key without picking up a tool, and how to change the lock yourself if you want a clean start.

Communal Area, Demised Asset: Where the Line Falls

The confusion usually comes from location. Because a bank of post boxes sits in a shared lobby or by the main entrance, residents assume the whole structure falls under the freeholder’s or the managing agent’s maintenance umbrella.

In most modern leases and building setups, there is a clear distinction:

• The bank of boxes (communal): the overall physical housing, the wall frame and the structure itself are the managing agent’s responsibility. If someone vandalises the casing or the bank comes away from the wall, that is a block maintenance issue covered by the service charge.

• The individual lock and key (demised): the specific lock cylinder, key and internal compartment assigned to your flat are almost universally demised to your individual property.

Because access to your post is private to your flat, managing agents do not hold spare keys to individual post boxes, for security and privacy reasons. If you lose your key, snap it off in the barrel or need the lock replaced, the responsibility — and the cost — sits with the flat owner or tenant.

Step 1: The Zero-Tool Fix (Ordering a Key by Code)

Before you break out the heavy tools or force the lock, check whether you can simply order a replacement key. Most post box locks are stamped with a unique code on the metal face of the keyway.

Specialist online suppliers (such as ReplacementKeys, FastKeys or CutKeysDirect) cut and dispatch replacement keys strictly from those numbers.

• Look for the code: inspect the front cylinder face where the key goes in. You will usually see a short combination of letters and numbers (e.g. CC102, FM45, or a four-digit number like 6801).

• Identify the brand: check for a small logo stamped next to the code. The major manufacturers — Lowe & Fletcher (L&F), Eurolocks, Ronis, Yale, Renz — use standardised key code series.

• Order online: searching the full code along with the manufacturer name (or uploading a photo of the lock face if there is no brand name) will usually turn up a matching key for a few pounds, delivered to your door.

Step 2: The Physical Fix (Replacing the Lock Yourself)

If the key code has worn off, the mechanism is jammed, or you simply want a new lock for peace of mind, you can swap the barrel out entirely. Post box locks (commonly called cam locks or cabinet locks) are simple, inexpensive and easy to service.

Opening a Locked Post Box (Without a Key)

If you are locked out and have no usable code, you rarely need to drill the lock out. Standard residential post box locks use soft brass internal wafers.

1. Take a medium-to-large flat-head screwdriver and insert the tip firmly into the keyway.

2. Apply firm forward pressure into the keyway while twisting the screwdriver with force in the direction the lock normally turns.

3. The leverage will shear the internal wafers, allowing the barrel to turn and retract the latch inside.

Caution: always make certain you are forcing open the box assigned to your own flat. If you are a tenant, drop a quick courtesy note to your landlord or agent first.

Removing the Old Cylinder

Once the post box door is open, look at the reverse of the lock mechanism on the inside of the door:

• Unscrew the small nut holding the flat metal latch (the cam) to the back of the lock cylinder.

• Remove the main retaining clip (a horseshoe-shaped metal slide) or the large hexagonal nut holding the barrel flush against the door.

• Pull the old barrel straight out through the front of the door.

Step 3: Measuring for the Replacement

You can buy replacement cam locks at almost any hardware store or online. Buying the correct size is the part people get wrong.

The key measurement is the length of the lock barrel: the distance from the back of the front rim to the start of the thread where the latch attaches.

• Common barrel lengths run from 16mm to 30mm.

• If the barrel is too short, the locking nut inside will not catch the door, or the latch will not reach the frame slot.

• If the barrel is too long, the latch sits too far back inside the box and spins loosely behind the frame catch without holding the door shut.

Installing the New Lock

1. Insert the new cylinder through the front of the post box door.

2. Secure it tightly from behind with the supplied retaining clip or hex nut.

3. Attach the metal latch (cam) to the back of the barrel and tighten the tail screw.

4. Test the key several times with the door open to check the latch rotates smoothly, then close the door and confirm the latch engages firmly behind the box frame.

Keeping a spare post box key somewhere sensible in the flat is always good practice. But whether you photograph the code on the lock face or spend ten minutes with a screwdriver and a simple cabinet lock, sorting out your flat’s mail access is straightforward once you know where the boundary lies.