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Lock Security GuideDeadlocks Explained: Types, Security Ratings and When Your Door Needs One
Written by Our Locksmith · Professional Locksmiths · South London · 7 min read
A deadlock is one of the most important security features on any timber door — yet many homeowners are unsure exactly what it does, or whether the lock they have meets their insurer's requirements. If your policy refers to a "5-lever mortice deadlock to BS3621," knowing what that actually means could save you from a refused claim. At Locksmith South London, our lock change team fits and upgrades deadlocks every day — this guide covers everything you need to know.
Unlike a night latch, which springs shut when you close the door, a deadlock bolt only moves with a key. That means even if a burglar breaks a nearby glass panel, they cannot reach in and turn a knob to open the door. Combined with anti-snap cylinder protection, a quality deadlock is one of the most cost-effective security upgrades you can make. Fixed price, no call-out fee, DBS checked.
What Is a Deadlock?
A deadlock is a type of lock where the bolt is completely fixed in position unless you turn a key. There is no spring mechanism — the bolt does not retract when you push the door. This is what makes it "dead." Once thrown, the bolt stays locked until you actively unlock it with the correct key from inside or outside.
In practical terms, this means a burglar who breaks a glass panel near the door cannot simply reach in and pull a handle to get in — because there is no handle-operated release. The door stays firmly closed until the right key is used. This is a critical advantage over standard spring latches, which can sometimes be opened from inside without a key.
How a Deadlock Works
Inside the lock, a series of levers must be lifted to precisely the correct height by the key before the bolt can be drawn back. A 5-lever deadlock requires five levers to align correctly — making it far more resistant to picking than a 2-lever version. The bolt itself extends into a reinforced steel striking plate in the door frame, anchoring the door securely.
Most deadlocks in the UK are mortice deadlocks — meaning the lock body is morticed (cut) into the edge of the door itself, so nothing protrudes. This makes them very difficult to attack compared to surface-mounted rim locks. For lock change services in South London, our City & Guilds locksmiths fit mortice deadlocks to a professional standard.
Deadlock vs Deadbolt vs Night Latch — What's the Difference?
These three terms are often used interchangeably but they describe different things. Understanding the difference helps you know exactly what lock you have — and whether it meets your insurer's requirements.
Mortice Deadlock (UK standard)
Fitted inside the door edge. Bolt moves only with a key. The most secure type for timber doors. BS3621 5-lever version required by most UK insurers.
Deadbolt (American / surface-mounted)
The US equivalent of a deadlock. Works on the same key-only principle but often surface-mounted. Less common on UK timber doors but used in some modern builds.
Night Latch (Yale-type)
Springs shut when you close the door — no key needed to lock it from outside. Convenient but not sufficient alone for insurance. Should always be used alongside a 5-lever deadlock.
The safest setup for a timber front door is a BS3621 5-lever mortice deadlock in combination with a night latch. If you are unsure what lock you currently have, our South London locksmiths can inspect and advise on the same visit.
5-Lever vs 2-Lever Mortice Deadlocks: Why It Matters for Insurance
Not all mortice deadlocks are equal. The number of levers inside the lock body directly affects its security rating — and whether it meets BS3621 British Standard.
2-Lever Deadlock
Only two levers must align for the bolt to move. Relatively easy to pick. These are typically found on garden gates, sheds, and internal doors — they are not suitable for external doors and will not satisfy a home insurance requirement for BS3621.
5-Lever Deadlock (BS3621)
Five levers must align precisely. A BS3621-certified 5-lever lock must also pass anti-pick, anti-drill, and anti-saw tests. This is the standard required by the vast majority of UK home insurance policies. Look for the kitemark on the lock body — it confirms the lock passed independent testing.
Insurance tip
Check your home insurance policy for the phrase "5-lever mortice deadlock to BS3621." If your current deadlock is only 2-lever, your insurer may refuse a burglary claim. Our locksmiths carry BS3621 stock and can upgrade on the same day — from £135 fitted.
Where Should You Fit a Deadlock on Your Home?
Deadlocks are primarily used on external timber doors — front doors, back doors, and side gates leading to the rear of the property. Here is where they should and should not be fitted:
Where to use a deadlock
- Timber front doors
- Timber back and side doors
- Internal security doors (between garage and house)
- Wooden garden gates with a timber frame
Not suitable for
- uPVC or composite doors (use multipoint locks instead)
- Aluminium-framed doors
- Fire escape doors (specialist hardware required)
- Doors thinner than 44mm (check with a locksmith first)
Correct Fitting Height
A mortice deadlock should be positioned roughly one-third from the bottom of the door — typically around 900mm–1000mm from the floor. This positioning maximises the mechanical advantage of the bolt and minimises leverage attacks. Our locksmiths always check door thickness, frame condition, and timber quality before fitting to ensure the lock performs as designed.
For uPVC door security issues, deadlocks are not the right solution — those doors rely on multipoint locking mechanisms fitted to the door itself.
Deadlock Brands: ERA, Chubb, Union and Yale Compared
Choosing the right brand matters. All four major UK deadlock brands offer BS3621-certified 5-lever mortice locks, but they differ in build quality, key security, and price. Here is a practical summary:
ERA Fortress 5-Lever Deadlock
Best-value BS3621 lock. Widely stocked, solid anti-pick/anti-drill features. Good choice for budget-conscious upgrades. Our most commonly fitted brand for straightforward residential jobs.
Chubb 3G114 5-Lever Deadlock
The UK's best-known deadlock. Recognised by name on many insurance policies. High-quality lever springs and key security. Excellent choice where the policy specifically names Chubb.
Union 2134 5-Lever Deadlock
A strong mid-range option with good anti-drill protection. Popular in the trade for reliability and durability. Suitable for most residential and light commercial applications.
Yale Superior 5-Lever Deadlock
Yale's premium mortice deadlock range. Well-suited for doors where Yale night latches are already installed — matching key profiles can simplify day-to-day use. BS3621 certified.
Not sure which brand is right for your door? Our locksmiths carry all four brands and will recommend based on your door type, existing hardware, and insurance requirements. All fitted with a 12-month guarantee.
Deadlock Fitting Cost in South London
Deadlock fitting in South London costs from £135 — this includes a BS3621 5-lever mortice deadlock and professional fitting. There is no call-out fee and no hidden charges. The price is confirmed before work starts.
£135
Standard Deadlock
ERA / Union BS3621 5-lever, fitted including labour
£155
Premium Deadlock
Chubb or Yale Superior BS3621 5-lever, fitted including labour
£45
Strike Plate Upgrade
Hardened steel box striker, fitted to existing deadlock
All prices include VAT. We quote the full price on the phone before we attend. For households requiring both a deadlock and a night latch fitted on the same visit, we offer a combined rate — call for details.
For full pricing across all lock types, see our lock change South London page. DBS checked, fixed price, no call-out fee.
Frequently Asked Questions About Deadlocks
What is the difference between a deadlock and a deadbolt?
A deadlock uses a bolt that can only be moved with a key — there is no spring mechanism. In the UK, "deadlock" typically refers to a mortice deadlock fitted inside the door edge. A "deadbolt" is the equivalent American term and often describes a surface-mounted version. Both require a key to lock and unlock, unlike a latch which springs shut on its own. For most timber doors in South London, a mortice deadlock is the correct choice.
Do I need a 5-lever deadlock for home insurance?
Yes — most UK home insurance policies require a 5-lever mortice deadlock meeting BS3621 on your external doors. A 2-lever deadlock will not satisfy this requirement and could result in a refused burglary claim. Check your policy wording for phrases like "5-lever mortice deadlock to BS3621." Our lock change team can fit a compliant BS3621 deadlock from £135, same day.
Can a deadlock be picked or drilled?
A quality 5-lever mortice deadlock certified to BS3621 must pass anti-pick and anti-drill tests as part of its certification. Budget 2-lever locks offer far lower resistance. For maximum protection, choose a 5-lever BS3621 lock from ERA, Chubb, or Union combined with a hardened steel box striker plate in the door frame. Our locksmiths can assess your current setup and advise on any weak points.
Should I use a deadlock and a night latch together?
Yes — this is the recommended combination for most timber front doors. The night latch provides slam-shut convenience (no key needed to lock it from outside) while the deadlock delivers the secure, key-only bolt required by insurers. Both should ideally meet BS3621. Our locksmiths can fit both locks in a single visit. See our guide on British Standard locks for full details.
How much does it cost to fit a deadlock in South London?
Deadlock fitting in South London costs from £135, including a BS3621 5-lever mortice deadlock and professional installation. There is no call-out fee and the full price is confirmed before we start. Premium brands such as Chubb or Yale Superior start from £155 fitted. Call or WhatsApp for a no-obligation quote.
Our Locksmith
Professional Locksmiths · South London
Our team of qualified locksmiths has been serving South London for over 10 years, specialising in BS3621 deadlock installations, anti-snap cylinder upgrades, and uPVC door repairs. DBS checked and fully insured.
Need a Deadlock Fitted in South London?
We're available 24 hours a day, 7 days a week. No call-out fee. DBS checked, City & Guilds certified. BS3621 deadlocks from £135.
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