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Understanding Door Locks: Which One Suits Your Door
At Trade Door Handles we offer a large range of door locks and latches for every situation, from low and high security through to internal and external use, across commercial and domestic properties. Supplied by Trade Door Handles, trusted UK supplier of architectural ironmongery since 1976, with quick nationwide delivery.
Choosing the right lock is not just about appearance. The wrong door lock type on the wrong door can leave a property under-secured, invalidate an insurance policy, or simply fail to fit. This guide walks through every major type of door lock sold in the UK today, where each one belongs, and how they compare, so you can order with confidence.
Mortice Locks: The UK Standard for Wooden Doors
A mortice lock sits inside a pocket cut into the edge of the door, rather than being surface-mounted, which makes it neater and harder to force than many alternatives.
2 and 3 Lever Locks
2 and 3 lever mortice locks are generally thinner, so they are ideal for internal doors, which are usually around 35mm thick. The lever count refers to the number of flat metal levers stacked inside the lock case that the key has to lift to the correct height before the bolt will move - a 2 lever lock has two of these gates, a 3 lever lock has three, and each extra lever adds another combination the key has to match, which is why 3 lever versions are considered a small step up from 2 lever, though neither is intended as a serious security barrier. Because the mechanism is simpler and shallower than a 5 lever case, 2 and 3 lever locks fit comfortably into a 35mm door without weakening the timber, which is exactly the thickness used for most internal doors in UK homes.
You'll find them on bedroom, study, living room and cupboard doors, anywhere the job of the lock is to give someone privacy rather than to stop a break-in. A typical use case is a keyed lock on a home office or bedroom door where you want to be able to lock it when you're out, or a nightly lock on a teenager's or guest bedroom - the kind of situation where the lock is doing a social job, not a security job. They are usually supplied with a pair of keys and, being a mortice type, sit fully inside the door edge so only the keyhole and the handle furniture are visible from either face. Browse the full range of 3 Lever Sash Locks for internal doors.
5 Lever Locks
5 lever mortice locks are the standard for external doors, which are usually 44mm thick or more, since that extra thickness is needed to house the larger, more complex lock case. Inside a 5 lever lock, the key has to lift five separate levers to the exact height required before the bolt will throw, and to meet the British Standard the lock also needs to pass tests for drilling, cutting and lock-picking resistance, plus a minimum number of possible key differs (usually upwards of 1,000, so no two locks from a batch share a working key). This is what most UK home insurers mean when they specify a British Standard 5 lever mortice lock (BS3621) as a minimum requirement for front and back doors - it isn't simply "a lock with five levers", it's a lock that has been independently tested to that standard, and you should look for the BS kitemark stamped on the faceplate to confirm it. Fitting a lock that hasn't been tested to BS3621, even one with five levers, can still leave a claim open to being challenged, so it's worth checking the specification rather than assuming any 5 lever lock qualifies. See our range of 5 Lever Sash Locks built to this standard.
A sash lock is not a separate category of lock in its own right - it describes the case construction, where a latch and a deadbolt are built into a single lock body rather than fitted as two separate units. The latch is the spring-loaded part that lets the door close and stay shut without being locked, operated by turning the handle, while the deadbolt is the square-section bolt that only the key can move, giving you the locked function. Both the 2/3 lever and 5 lever ranges above are sash lock versions, which is why you'll usually order them by lever count and door thickness (for example "3 lever sash lock, 64mm case, 35mm door") rather than by a separate "sash lock" specification.
Euro Profile and Oval Profile Locks
Euro profile and oval profile locks work differently to a traditional mortice lock. Instead of a fixed lever mechanism built into the lock case, they use a removable cylinder that slots through the door and lock body, operated by a key on one or both sides.
- Euro profile cylinders have a flat profile and are the most common type fitted to UK composite and uPVC doors, as well as many timber doors with multi-point locking.
- Oval profile cylinders have a rounded, oval-shaped profile and tend to appear on older or European-style door systems.
- Both allow the cylinder to be replaced on its own if a key is lost, without changing the whole lock body.
Take a look at our Euro Profile Sash Locks if you are replacing or upgrading a cylinder lock.
Bathroom Locks and Tubular Deadbolts
Bathroom locks are generally used on bathroom, WC or en-suite doors rather than external doors, since they are built for privacy rather than security. Most versions are a simple turn-and-release mechanism operated from inside, with an emergency release slot on the outside in case a child locks themselves in.
A tubular deadbolt is a compact cylindrical bolt often paired with a bathroom lock or fitted as a standalone privacy bolt on internal doors. It is quick to fit and does not need the same depth of mortice as a full lock case, which makes it a popular choice for thinner internal doors. Our Bathroom Locks and Deadbolts collection covers both.
Rim Locks, Rim Latches and Night Latches
Rim locks and rim latches are surface-mounted onto the face of the door rather than being sunk into it. They are often used in traditional properties, listed buildings, or on very thin doors where a mortice cannot be cut without weakening the timber. Because they sit on the surface, they also tend to suit period ironmongery styles better than a modern mortice lock. Browse our Rim Locks and Rim Latches range.
A cylinder night latch (sometimes just called a "Yale lock") is a specific type of rim lock. It automatically locks when the door is closed, can be opened from inside with a handle or knob, and needs a key from outside. Night latches are commonly fitted as a secondary lock alongside a 5 lever mortice lock on front doors, since insurers often want both.
DIN Locks, Sliding Door Locks and Multi-Point Systems
DIN locks follow a German industry standard (Deutsches Institut fur Normung) for lock case dimensions and backset, and are widely used across Europe. If you are replacing a lock on an imported door, a DIN lock is usually the correct match rather than a standard UK mortice size. See our DIN Locks range for standard DIN sizes.
Sliding door locks are built specifically for sliding or patio doors, where a traditional swinging mortice case will not work. They typically hook or bolt into a strike plate rather than extending a straight bolt, since a sliding door moves sideways rather than swinging shut. Our Sliding Door Locks collection is built for this application.
Multi-point locking systems engage several bolts, hooks or rollers around the frame at once, usually operated by lifting the handle and turning a euro cylinder key. They are standard on composite and uPVC doors and offer a higher level of security than a single mortice lock, since forced entry has to overcome multiple locking points rather than one.
Digital Locks and Modern Security
Comparing Door Lock Types
| Lock type | Best for | Security level |
|---|---|---|
| 2/3 lever mortice | Internal doors | Privacy only |
| 5 lever mortice (BS3621) | External timber doors | Insurance-rated |
| Euro/oval profile | uPVC, composite, multi-point doors | Medium-high |
| Rim lock / night latch | Period doors, secondary lock | Medium |
| Multi-point system | Composite and uPVC doors | High |
| Digital lock | Lets, rentals, shared access | Varies by model |
As a general rule: the older or thinner the door, the more likely you need a mortice or rim solution; the newer the door, particularly uPVC or composite, the more likely it already takes a euro profile cylinder and multi-point gearbox.
How to Make Your Home More Secure
A few practical steps make the biggest difference to home security, beyond simply picking a lock:
- Fit a BS3621-rated 5 lever mortice lock to external timber doors wherever your insurer requires it.
- Pair a mortice lock with a night latch for a two-lock front door setup.
- Check euro cylinders are anti-snap rated, since cylinder snapping is one of the most common forced-entry methods on uPVC doors.
- Keep multi-point gearboxes lubricated so all locking points engage fully every time the door closes.
Locks for Fire Doors and Let Properties
Fire doors need hardware that has been tested as part of a certified door set, so any lock, latch or hinge fitted must carry the correct fire rating for that door - swapping in a standard lock can invalidate the fire certification. If you manage an Air B&B, guest house or another let property, a digital lock or coded access system is usually the most practical option, since it lets you change access codes between guests without re-keying the whole property.
Frequently Asked Questions
What is the difference between a 2, 3 and 5 lever door lock?
The lever count is the number of levers inside the lock that the key has to lift to the correct height before the bolt will move. 2 and 3 lever locks are lighter duty and suited to internal doors, while 5 lever locks contain more levers, are harder to pick, and are the type most UK insurers require on external doors.
What is a euro profile lock?
A euro profile lock uses a removable cylinder with a flat profile that passes through the door and lock case. It is the standard cylinder type used on UK uPVC and composite doors and can be replaced independently of the lock body.
What is a DIN lock?
A DIN lock follows the German DIN standard for lock case dimensions and backset, commonly used on doors manufactured to European sizing rather than standard UK measurements.
Can I put a standard lock on a fire door?
Fire doors must use hardware tested and certified as part of that specific door set. Fitting a lock that is not fire-rated for the door can invalidate its fire certification, so a certified fire door lock should always be used.
What type of lock is best for a let property or Air BnB?
Digital locks with a keypad or coded access are commonly used on let properties and guest houses, as the access code can be changed between guests without replacing the lock or cutting new keys.
What is a multi-point locking system?
A multi-point locking system engages several bolts, hooks or rollers around the door frame at once when the handle is lifted and the key turned, offering higher security than a single-point mortice lock. It is standard on most uPVC and composite doors.
Summary
There is no single "best" door lock - the right choice depends on the door, its thickness, and how the property is insured and used.
Internal doors generally suit a 2 or 3 lever mortice lock, since privacy matters more than forced-entry security.
External timber doors need a 5 lever mortice lock certified to BS3621, which most UK home insurers require as a minimum.
Modern uPVC or composite doors will already be set up for a euro or oval profile cylinder paired with a multi-point locking system.
Period properties or doors needing a secondary lock usually suit a rim lock or cylinder night latch rather than a mortice case.
Bathroom and internal privacy doors are best served by a bathroom lock or tubular deadbolt rather than a full security lock.
Rented, let or multi-occupancy properties are increasingly moving to digital locks, so access codes can be changed between tenants or guests without re-keying the door.
If you are not sure which type of door lock suits your door, our team at Trade Door Handles can help you match the correct lock body, backset and finish before you order.
