Do I need both a Yale and a mortice lock on my front door?

For a wooden front door, yes. The nightlatch provides everyday convenience by allowing you to close the door and have it latch automatically. The BS3621 mortice deadlock provides the security your insurance company requires. Having both gives you the best combination of security and practicality.

How do I know if my mortice lock is BS3621?

Look at the faceplate on the edge of the door. A genuine BS3621 lock will have the BS3621 number stamped on it along with the BSI Kitemark — a heart-shaped symbol. If you cannot see these markings, the lock probably does not meet the standard. Some older locks carry a BS number but not the Kitemark, which means they were not independently tested.

Can a locksmith fit a mortice deadlock to any wooden door?

Most wooden doors can accept a mortice deadlock, but the door needs to be thick enough — at least 44mm for a standard BS3621 lock. Very thin doors or hollow-core internal doors are not suitable. I always assess the door on-site before starting work and will advise if there are any issues.

What is the difference between a 3-lever and 5-lever mortice lock?

A 3-lever mortice lock has three internal levers and offers fewer key combinations, making it easier to pick or bypass. A 5-lever mortice lock has five levers, providing significantly more key combinations and resistance to manipulation. Insurance companies require a 5-lever lock to the BS3621 standard. I always recommend upgrading any 3-lever lock to a 5-lever BS3621.

Yale Locks vs Mortice Deadlocks: Which Does Your Front Door Need?

Most UK front doors have a Yale nightlatch on top and a mortice deadlock below. But do you need both? And what if you only have one? Here is the honest answer.

Yale Nightlatch vs Mortice Deadlock: What's the Difference?

This is one of the most common questions I get from customers across [Coventry](/areas/coventry-city-centre), and the answer matters more than most people realise. The short version: they do different jobs, and most front doors should have both.

I'm Ross, a local locksmith, and I've fitted thousands of both types across the city. Let me explain exactly what each one does, why they matter, and which one your door actually needs.

What Is a Yale Nightlatch?

A Yale nightlatch — often just called "a Yale" — is the lock you can slam shut. It has a spring-loaded latch bolt (the curved bit that clicks into the frame) and sits on the inside surface of the door. The cylinder (where you put the key) pokes through from the outside.

When you close the door, the latch springs into position and the door is held shut. You can open it from inside using the handle without a key. From outside, you need the key.

How a Nightlatch Works

The **latch bolt** is spring-loaded and bevelled so the door can be pulled shut

A **snib** on the inside lets you hold the latch back (to leave the door on the latch) or lock it in the deadlocked position

Standard nightlatches can be opened by slipping a credit card or strip of plastic between the door and frame — this is called **loiding**

**Deadlocking nightlatches** have a secondary bolt that, when the door is fully closed, prevents loiding

Common Types

**Yale 85** — basic rim nightlatch, no deadlock function. Not secure enough for a front door.

**Yale 89** — deadlocking version, much better. The small secondary bolt deadlocks the latch when the door is closed.

**ERA and Union equivalents** — similar products from other manufacturers.

**British Standard nightlatches** — BS8621 rated versions that can be unlocked from inside without a key (fire safety feature).

What Is a Mortice Deadlock?

A mortice deadlock is a lock fitted inside the body of the door. "Mortice" means it sits in a rectangular pocket (mortice) cut into the edge of the door. "Deadlock" means the bolt doesn't spring — it's thrown by the key and stays locked until you turn the key again.

How a Mortice Deadlock Works

The **deadbolt** is a solid rectangular bolt, typically 20mm throw on BS3621 locks

Inside, there are **five levers** — flat metal plates that must all be lifted to the correct height by the key before the bolt will move

The key has a pattern of cuts that corresponds to the lever positions — this is why mortice keys look so distinctive

Once locked, the bolt cannot be pushed, slid, or forced back without the correct key

The BS3621 Standard

The [BS3621 standard](/blog/five-lever-mortice-deadlock-guide) is the benchmark for mortice deadlocks. A lock carrying this certification has been independently tested for:

Pick resistance

Drill resistance (hardened steel plates protect the levers)

Bolt strength — the bolt resists sawing and forcing

Key security — at least 1,000 key combinations (differs)

The bolt throws at least 20mm

This is the lock your insurance company almost certainly requires on your wooden front door. If you don't have one, you may not be covered for theft. More on this below.

Why Most Front Doors Should Have Both

A nightlatch gives you convenience — you can shut the door behind you quickly, and it latches automatically. But it's not a high-security lock. Even a deadlocking nightlatch can be defeated by a determined intruder.

A mortice deadlock gives you security — once that bolt is thrown, it takes serious force or the right key to open the door. But you have to remember to lock it with the key every time.

The combination of both covers your bases:

The nightlatch keeps the door closed and provides basic security for everyday use (popping to the shops, answering the door)

The mortice deadlock provides genuine security when you leave the house or go to bed at night

Insurance companies expect both — a BS3621 mortice deadlock is the minimum, and a nightlatch is the practical, everyday lock

I'd estimate that at least half the wooden front doors I look at in Coventry — in areas like [Cheylesmore](/areas/cheylesmore), [Styvechale](/areas/styvechale), and [Earlsdon](/areas/earlsdon) — are missing one or the other. Sometimes the mortice deadlock is there but it's an old 3-lever version that doesn't meet BS3621. Sometimes there's only a nightlatch.

Common Misconceptions

"My Yale lock is enough"

No. A nightlatch on its own is not sufficient security for a front door. It can be shimmed, loided (credit card trick), or the cylinder can be attacked. It should always be paired with a mortice deadlock.

"I don't need a mortice lock because my door is strong"

The strength of the door is irrelevant if the lock can be bypassed. A strong door with a weak lock is like a safe with the combination written on it.

"My lock has 'BS' on it so it's fine"

Not necessarily. Older BS3621 locks may have been superseded, and some locks carry a BS number for a different standard. Look for the **BSI Kitemark** — the heart-shaped symbol — alongside the BS3621 marking. That confirms independent testing.

"Mortice deadlocks are old-fashioned"

They're traditional, but the engineering is sound. A quality five-lever mortice deadlock fitted properly to a solid door is extremely secure. There's nothing old-fashioned about effective security.

When to Upgrade

You should consider upgrading your locks if:

You only have a nightlatch on your front door — add a BS3621 mortice deadlock

Your mortice lock is a 2 or 3-lever type — upgrade to a 5-lever BS3621

Your nightlatch is a basic non-deadlocking type — upgrade to a deadlocking version or BS8621

You've moved into a new property — [change the locks](/services/lock-change) immediately, because you don't know who has keys

Your locks are visibly worn, stiff, or difficult to operate

Your insurance company has specified requirements you're not meeting

What About uPVC and Composite Doors?

If you have a uPVC or composite door rather than a wooden one, this whole discussion doesn't apply to your door. uPVC and composite doors use [euro cylinder locks](/blog/euro-cylinder-locks-explained) in a multipoint locking system, and the main concern there is [lock snapping](/blog/what-is-lock-snapping). The upgrade path is an anti-snap euro cylinder, not a mortice deadlock.

Prices and What to Expect

Here's what I charge for the most common jobs:

**Fitting a BS3621 mortice deadlock** (new mortice cut) — from £79 fitted

**Replacing an existing mortice deadlock** with BS3621 — from £69 fitted

**Upgrading a nightlatch** — from £59 fitted

**Both locks fitted to a new door** — I'll quote on-site depending on the door

I carry stock of all the main brands — Union, ERA, Yale — in my van, so most jobs are completed in a single visit. Call 07735 336175 for a quote or check the [prices page](/prices).

The Bottom Line

If you have a wooden front door, you need both a nightlatch and a BS3621 mortice deadlock. The nightlatch gives you everyday convenience. The mortice deadlock gives you security and keeps your insurance valid. One without the other is a compromise, and door security is not something you want to compromise on.

If you're not sure what locks you have, or whether they meet the required standards, I'm happy to take a look. Call 07735 336175 — I cover the whole of Coventry and I'll give you an honest assessment with no obligation.