Addiscombe Locksmith Service Team
Local locksmith team
7 Oct 2026 12 min read
If you look at most front doors in Croydon — whether a Victorian terrace off London Road, a 1930s semi in Shirley, or a purpose-built flat near East Croydon station — you will usually find two separate locks. One sits about a third of the way down the door and operates with a chunky key. The other is closer to the top and often snaps shut on its own when the door closes. Both do important jobs, but they work in completely different ways, and knowing the difference matters when you are choosing insurance-compliant security or trying to explain what has gone wrong to a locksmith Croydon.
This guide explains what a mortice lock is, how a nightlatch (sometimes called a Yale lock or rim lock) works, why most UK insurers want both on your front door, and what to do if either one fails. By the end, you will have a clear picture of what is behind your door and what questions to ask next time you need a lock change Croydon or a door lock replacement Croydon.
## What Is a Mortice Lock — and What Makes It Different?
[4] A mortice lock is a lock that fits inside a pocket — called a mortice — cut into the edge of the door itself. Because the entire lock body sits within the door, nothing protrudes on the face of the door except the keyhole escutcheon and the bolt. When you turn the key, a rectangular bolt (called a deadlock bolt) shoots directly into a metal keep fixed to the door frame. There is no spring mechanism; the bolt only moves when you use the key. That is what makes it a deadlock — it cannot be pushed back without the correct key. A mortice lock is what most people are referring to when they ask what is a mortise lock or what is a mortice lock, so the two spellings cover exactly the same type of lock.
The number of levers inside the lock is what determines its security rating. A 2 lever mortice lock is a basic option sometimes found on internal doors or old sheds, but it offers minimal resistance to picking and is generally not acceptable to home insurers for external doors. A 5 lever mortice lock is the standard for a front or back door in the UK. Many UK home insurance policies explicitly require a 5 lever mortice lock that meets British Standard BS3621, and insurers sometimes ask to see this if you make a claim. If your door has an older or lower-grade lock, a lock change Croydon to bring it up to BS3621 standard is a straightforward job for an experienced locksmith.
## How a Nightlatch (Rim Lock) Works — the Other Lock on Your Door
The lock near the top of your front door is almost certainly a nightlatch, often called a Yale lock after one of the most familiar makes. Unlike a mortice lock, a nightlatch is a rim lock — meaning it is surface-mounted on the inside face of the door rather than sunk into it. The main body of the lock sits on the door's inner face, while a small cylinder passes through the door to the outside. What is a rim cylinder? It is the round barrel you can see on the outer face of the door, usually about the size of a 50p coin, into which you insert your key from outside. When you turn the key, it rotates the cylinder and retracts the spring-loaded latch. From inside, you can open the door with a simple thumb-turn or handle without needing a key at all.
The convenience of the nightlatch is precisely what limits its security when used alone. The spring latch can be pushed back with a credit card or similar flat tool if the door frame is not tight. Most nightlatches have a deadlocking feature — a small button or slide on the inside that locks the latch in the closed position and prevents it being slipped — but this only helps if you remember to use it. This is why a nightlatch works as a convenience lock for going in and out during the day, while the mortice lock below it is what you engage last thing at night or when you go out for more than a few minutes.
## Why UK Front Doors Usually Have Both — and What Happens When One Fails
[5] The combination of a 5 lever mortice lock and a nightlatch gives you two independent layers of security operating in different ways. If someone manages to manipulate the nightlatch latch, they still face the deadlock bolt of the mortice lock, and vice versa. That is why insurance companies and most security advice in the UK recommends both. On uPVC and composite doors — now common in Croydon across areas like Addiscombe, Selhurst, and New Addington — the arrangement is different. These doors use a multipoint locking system operated by lifting the handle, which throws multiple bolts into the frame simultaneously, usually driven by a euro cylinder that replaces both the traditional mortice and nightlatch in one mechanism.
Euro cylinders come with their own risks: a well-documented method of attack called cylinder snapping can defeat a standard cylinder in seconds. If your uPVC door uses a euro cylinder, upgrading to an anti-snap, TS007 3-star rated cylinder is one of the most cost-effective security improvements you can make. When either type of lock fails — whether the mortice bolt is seized, the nightlatch cylinder is worn, or a uPVC cylinder has snapped after a break-in attempt — you need upvc door lock repair Croydon or a full door lock replacement Croydon carried out promptly. A faulty lock is not just inconvenient; a door that cannot be properly secured is a risk to your household overnight. If you are in this situation right now, our team operates as a 24 hour locksmith Croydon and can usually reach you within about 30 minutes — call 020 4542 3118 and we will confirm the exact price before anyone sets off.
## Choosing the Right Lock for Your Front Door: Practical Guidance
[6] If you are replacing or upgrading a mortice lock on a timber front door, the starting point is confirming the lever count and checking the BS3621 stamp. You can often see this on the lock backplate. A 5 lever mortice lock that meets BS3621 is the minimum recommended for insurance compliance on most standard policies. If you are replacing only the cylinder on a nightlatch — perhaps because you have lost a key and want to prevent unauthorised entry — a qualified locksmith can swap the rim cylinder without touching the rest of the lock, restoring security quickly and cleanly. The same logic applies to an exterior door knob with lock and key on some older doors: the cylinder can often be changed independently, and changing the cylinder means the old keys simply stop working.
On uPVC and composite doors, the conversation shifts to multipoint locks and euro cylinders. The key measurements here are the cylinder size — the distance from the centre fixing screw to each end, stated in millimetres — so the replacement cylinder sits flush with the door furniture rather than protruding, which itself is a snapping risk. If you are unsure what you have, a locksmith Croydon from our team can assess your door furniture, measure up, and recommend the right grade of cylinder for your door. The final price will depend on the lock type, parts required, and the time of day you call — we will always confirm the exact figure up front before work begins.
## Locked Out, Lock Changed, or Just Unsure? What to Do in Croydon
If you are locked out Croydon and cannot get in, start with the basics: check whether a window is open, whether a neighbour holds a spare key, or whether there is another entrance to the property. Do not attempt to force the lock yourself — aside from the risk of injury, you are likely to damage the door, the frame, or the lock in a way that costs more to repair than a professional call-out. If you are a tenant, your letting agent or housing association may have an emergency contact. If none of those options apply, the right move is to call an emergency locksmith Croydon who can open the door using non-destructive methods wherever possible, then advise you on whether the lock needs replacing afterwards.
Beyond lockouts, our team handles the full range of residential lock work across Croydon and surrounding areas including Thornton Heath, Purley, Coulsdon, and Kenley: fitting new 5 lever mortice locks to BS3621 standard, replacing worn or damaged nightlatch cylinders, carrying out upvc door lock repair Croydon on seized or misaligned multipoint locks, upgrading standard euro cylinders to anti-snap 3-star rated versions, and advising on whether a full door lock replacement Croydon is the better option when a lock has been compromised. We are a mobile locksmith Croydon service, which means we come to you — no shop visit needed, and no waiting around. Call 020 4542 3118 at any hour, day or night, seven days a week including bank holidays, and we will send a skilled locksmith straight away.
## 25 Lock and Door Security Services We Carry Out in Croydon
Here is a full picture of the work we carry out for homeowners, tenants, and landlords across Croydon and the surrounding postcodes (CR0, CR2, CR3, CR4, CR5, CR7, CR8, SE25): 1. Emergency lockout opening — non-destructive entry where possible. 2. 5 lever mortice lock supply and fitting (BS3621). 3. 2 lever mortice lock upgrade to 5 lever. 4. Nightlatch cylinder replacement. 5. Full nightlatch (rim lock) replacement. 6. Anti-snap euro cylinder upgrade. 7. TS007 3-star cylinder fitting. 8. Multipoint lock repair on uPVC doors. 9. Multipoint lock replacement on uPVC doors. 10. Composite door lock repair. 11. uPVC door lock repair Croydon — gearbox replacement. 12. Door lock replacement Croydon — full lock set change. 13. Broken key extraction from mortice lock. 14. Broken key extraction from nightlatch cylinder. 15. Snapped cylinder removal and replacement. 16. Door alignment adjustment (door dropping or binding affecting lock operation). 17. Lock change after lost or stolen keys. 18. Lock change after a break-in. 19. Additional lock fitting to improve front door security. 20. Back door mortice lock fitting. 21. Communal entrance lock assessment for blocks of flats. 22. Flat front door lock change. 23. Boarding up after door damage (temporary security). 24. Security survey and lock recommendation for newly rented properties. 25. Landlord lock change between tenancies. Each job begins with a clear up-front quote — the price depends on the lock type, parts required, time of day, and distance — so there are no surprises on completion.
Frequently asked questions
What is the difference between a mortice lock and a nightlatch?+
[7] A mortice lock sits inside the door — cut into the edge of the door itself — and uses a deadlock bolt that only moves with the correct key. A nightlatch (or rim lock) is surface-mounted on the inside face of the door and has a spring latch that closes automatically when the door shuts. You operate the nightlatch from outside with a key in the rim cylinder and from inside with a thumb-turn. Because the nightlatch latch is spring-loaded, it offers less resistance on its own; the mortice deadlock is what provides the stronger barrier when you are out or in bed. Most UK front doors use both.
Do I need a 5 lever mortice lock for home insurance?+
Most UK home insurance policies require a 5 lever mortice lock that meets British Standard BS3621 on the main entrance door. A 2 lever mortice lock is not normally acceptable on an external door for insurance purposes. If you are unsure what you have, check the backplate of the lock inside the door — a BS3621 compliant lock will usually show that standard. If your lock does not meet the requirement, a lock change to a compliant 5 lever mortice lock is straightforward, and an experienced locksmith Croydon can carry this out in a single visit.
My uPVC front door does not have a mortice lock — is it secure?+
uPVC and composite doors do not use a traditional mortice lock or nightlatch. Instead, they use a multipoint locking system driven by a euro cylinder. When you lift the handle and lock with the key, multiple bolts shoot into the frame at different points. This can be very secure, but the euro cylinder itself is a vulnerability if it is a standard grade — a technique called cylinder snapping can defeat it quickly. Upgrading to an anti-snap, TS007 3-star rated cylinder significantly improves resistance. If you are in Croydon and unsure about your cylinder grade, our team can assess it and recommend the right upgrade.
What should I do if I am locked out of my house in Croydon?+
First, check whether any other door or window is accessible, and whether a neighbour or family member holds a spare key. If you are a tenant, contact your letting agent or housing association emergency line. If none of those options work, call a professional emergency locksmith Croydon rather than attempting to force entry yourself — forced entry risks injuring you and can cause significant damage to the door and frame. Our team operates as a 24 hour locksmith Croydon, available every day including weekends and bank holidays. We will confirm the price on the phone before we set off so you know exactly what to expect. Call 020 4542 3118 and we will usually be with you within about 30 minutes.
