Guide
Types of Door Locks in the UK: What Each One Is and Where It Fits
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All UK Door Lock Types at a Glance
Most lock names come from one of two places: the complete mechanism, or the single component the key fits into. Mixing those two habits is how mortice lock, nightlatch, euro cylinder and multipoint lock end up being used as if they meant the same thing, when in fact each refers to a different part or system.
That matters the moment something goes wrong, because one of the earliest questions in any repair or replacement is what type of lock you have. The keyhole alone seldom answers it. The door does a better job: note what it is made from, where the mechanism is positioned, and what you can see on its inside face and along its edge. A mortice lock, a nightlatch, a rim cylinder and a multipoint locking system can be told apart using those observations. The main UK types are compared below.
| Family | Where it usually appears | Tell-tale sign | Defining feature |
|---|---|---|---|
| Mortice sashlock | Timber doors, entrance and internal | A recessed case in the edge with a spring latch and a locking bolt | It joins a latch worked by handles to a separate key-operated lock |
| Nightlatch with rim cylinder | Timber entrance doors in most cases | A box-shaped body on the inside face, and its cylinder visible outside | The latch will usually catch when the door closes |
| Mortice deadlock | Timber entrance doors in most cases | A recessed case in the edge, its bolt visible when the door stands open | A key-worked bolt and no handle-worked latch inside the same case |
| Surface-mounted rim lock | Some older timber doors, internal doors and outbuildings | The entire case is fixed where you can see it on the inside face | Surface-mounted rather than housed in the door edge |
| Euro cylinder in a single-point lock | Some timber, aluminium and metal doors | A euro-profile keyway, but no long strip or multiple locking points | The cylinder works a single central lock case |
| Euro cylinder in a multipoint lock | uPVC and composite doors, commonly | A euro-profile cylinder close to the handle, and a long strip on the edge | The cylinder accepts the key, and the wider mechanism controls several points |
These rows point to a general family and never to a precise model. Material is not decisive either: a modern timber door can use a multipoint, while aluminium and metal doors may have cylinder-operated lock cases. Choosing replacement parts requires product markings and measurements first. Further down, this guide explains each common UK type, how to identify it and what its components do, shows where to look for markings, and explains why appearance alone cannot settle the model or security standard. The middle columns are the ones most often misread, so each has its own section next.
Locks Fitted Into a Timber Door
A timber door usually carries one of two things: a lock buried in its edge, or a latch fixed to its inside face, and very often both. If the keyhole is in the edge of the door, you are looking at a mortice lock. If the key passes through the face into a box on the inside, it is a nightlatch. A surface-mounted rim lock is also possible, so the simplest test is whether the case sits inside the edge or can be seen on the inside face.
Mortice Deadlocks and Mortice Sashlocks
A mortice lock sits in a pocket cut into the edge. The deadlock version throws a bolt with the key and nothing else. The sashlock adds a spring latch worked by handles.
Nightlatches and Rim Cylinders
A nightlatch is the box on the inside face, turned from outside by a rim cylinder, and it normally latches as the door closes. An older surface-mounted rim lock looks similar but is not necessarily a nightlatch. Depending on its design, the case may hold a latch, a bolt or both, it may not latch by itself, and it may be worked by a key, a handle or a knob.
When a Door Has Both
Plenty of timber entrance doors carry a nightlatch and a separate mortice lock, working independently, so identify each on its own. Neither is better than the other; they do different jobs. Some timber doors also use a multipoint, a connected system more often seen on uPVC and composite doors, whose locking points move from the edge into frame keeps.
Multipoint Locks Are Not All One Type
A full-height locking strip sits along the edge of a uPVC or composite door, and its make cannot simply be exchanged for another. That strip is the multipoint assembly the handle operates. The euro cylinder is a separate component turned by the key. Someone asking about a uPVC door's lock type usually needs the identity and arrangement of the strip, rather than the cylinder alone.
The Strip Itself and What It Tells You
Start with the door safely open and inspect the visible faceplate. A multipoint links several securing positions to a central gearbox. Hooks, rollers, pins and bolts can appear in different combinations, with corresponding keeps fitted to the frame. This family is common on composite and uPVC doors and occurs on some timber and aluminium examples as well.
| Visible or connected part | What to understand |
|---|---|
| Central mechanism | The gearbox coordinates movement received from the handle and cylinder |
| Handle spindle | Connects the handles through the door and transfers their action to the gearbox |
| Cylinder | The keyed unit that activates the surrounding lock |
| Edge strip and faceplate | Connect the gearbox with locking components farther along the door |
| Projecting locking parts | Hooks, bolts, pins or rollers that locate into frame keeps |
| Keeps on the frame | Accept the latch and the relevant locking points |
Identification involves more than counting projections. Capture the manufacturer name or symbol, stamped references and any label near the latch. Note where the gearbox lies, which locking-point shapes are present and how they are spaced. Include clear photographs of the complete edge, handles, cylinder and markings when seeking help with identification.
PZ describes the separation of the handle spindle centre from the cylinder centre. Backset describes the cylinder centre's depth relative to the faceplate edge. Although useful clues, these dimensions can match on mechanisms with incompatible gearbox connections, faceplates or point positions. Replacement ordering needs accurate measurements, addressed in the separate guide covering cylinder changes.
The action also varies. Raising a handle often extends the locking parts, with a subsequent key turn preventing their release through the handle. Some strips instead engage on closure, while others use key movement to drive their locking points. Observing that action will not establish the manufacturer or exact model.
Treat symptoms as clues rather than a diagnosis. A key refusing to rotate can indicate cylinder trouble. Handle travel without movement at the strip can involve the spindle or gearbox. A lock that behaves normally while open but resists when closed may have a door or keep alignment problem. Stop forcing stiff components: wear, misalignment and internal faults can all create resistance, and additional force can increase damage. A fault in one part need not require replacement of the whole assembly.
Understand What Each Specification Proves
Descriptions often mix installation type, mechanism, lever number, dimensions, appearance and tested security. Recognising a single term cannot establish the entire specification.
| Term | Meaning in a description |
|---|---|
| Rim | The main body sits on the door's surface |
| Mortice | The case fits into a recess cut into the edge |
| Sashlock | A handle-operated latch shares its case with a deadbolt |
| Deadlock | A bolt mechanism without a spring-operated latch |
| Nightlatch | A surface-mounted unit that usually latches as the door closes |
| Case size | Mortice case depth, often stated in millimetres or inches |
| Backset | Faceplate-edge distance to the centre of the keyhole, spindle or cylinder |
| Finish | The external colour or treatment, such as chrome, brass or satin nickel |
Those terms describe families and dimensions, but a replacement can still differ at its spindle, keyhole, faceplate or fixing locations.
A cylinder recognises the inserted key and passes its rotation into the surrounding mechanism. That mechanism might be a mortice case, surface nightlatch or multipoint gearbox. Replacing the cylinder changes key access and can improve protection against some attacks, but it leaves gearbox wear, damaged strips, loose handles and alignment faults unresolved. If the complaint persists, the lock case, spindle, frame keeps and associated mechanism still need assessment.
Euro profiles are narrow with a rounded upper portion. They commonly serve composite, aluminium and uPVC doors, and occasionally timber ones. A cylinder with a single keyed face is a single cylinder; keys operating both faces identify a double version. A thumbturn uses an outside key and an inside turning knob. Usually an edge screw retains the cylinder as it passes through the door and gearbox. Choose length to suit the thickness occupied by the door and handles. An overly exposed outer end may be easier to attack physically.
An oval cylinder has a rounded oval shape and carries out a comparable job. It appears less frequently in new domestic installations but remains in existing doors and older mechanisms. Neither similar overall length nor similar function makes it interchangeable with a euro cylinder. The furniture opening and lock case must be intended for its profile. Establish the shape, complete length, fixing position and key or thumbturn arrangement on both faces. Problems involving stiffness, uncertain locking or handle movement also require checks beyond the cylinder. For a security upgrade, compare tested standards and resistance to picking, drilling, snapping and other attacks, since product features vary considerably.
Lever counts describe internal workings. The key must position a lever lock's internal levers at particular heights before its bolt can travel. Three-lever and five-lever labels state how many are present. A five-lever mortice sashlock therefore has a recessed case containing five levers, a latch and a deadbolt. Three-lever models often suit internal applications, while five-lever models are common on timber entrance doors. Materials, construction, bolt details and tested performance can differ even with identical counts. Entrance suitability and insurance requirements need more than that number.
A five-lever designation does not mean the lock satisfies BS 3621. Under BS 3621, mechanically operated single-point assemblies are assessed for thief resistance, with keys required to lock and unlock on each face. The assembly's tested performance determines compliance. The edition currently in force is BS 3621:2017+A1:2024. A reference normally appears on a compliant lock or its packaging, often accompanied by a certification mark. Read it in full because older hardware may cite an earlier edition, and verify the exact product model. Neither bolt length nor a recognisable brand substitutes for that evidence. Keyless opening from the inside may fall under a different standard, as BS 3621 specifically addresses exit by key.
Reading a Lock's Name
Read a lock listing left to right and it explains itself. In [Maker] five-lever mortice sashlock, the first word names the manufacturer, the second gives the number of levers, the third says the case is recessed into the door, and the fourth says it has both a latch and a deadbolt. Other listings add the case size, the finish or a security standard. These are separate facts about separate things, so recognising one term never confirms the complete specification. Note what is missing from the example: a five-lever mechanism does not in itself demonstrate compliance with BS 3621.
What Lever Counts Actually Mean
A lever-operated mortice lock has a set of internal levers that the key lifts to specific heights before the bolt can move, three in a three-lever lock and five in a five-lever lock. The count helps describe the mechanism but is not a full security assessment: locks with identical counts can differ in materials, construction, bolt design, attack resistance and tested performance. Three-lever locks are often fitted to internal doors, and five-lever locks are common on external timber doors, but the count alone should not be used to confirm suitability for an entrance door or an insurer's requirements.
Words and Measurements in a Listing
Mortice and rim say whether the case is recessed or surface-mounted. Deadlock means a bolt without a spring latch; sashlock means a deadbolt plus a handle-operated latch; nightlatch means a surface-mounted lock that normally latches when closed. Cylinder is the key-operated component; multipoint is a mechanism with locking points along the edge. Case size gives the mortice case's overall depth, backset the distance from the faceplate edge to the keyhole, cylinder or spindle centre, and finish the surface, for instance brass, chrome or satin nickel. These narrow the search without proving a part will fit.
The Faceplate Marking
Start with parts visible while the door is open; a mortice or multipoint faceplate may be stamped with a maker's name, logo, series or code. Handles carrying one maker's name may sit over another company's lock. Do not remove a lock case, gearbox or strip to look for numbers, and check type and measurements before ordering.
Which Door Each Type Belongs On
Door First, Lock Second
Every type in this guide is explained by one rule: the door decides the lock. Read the door and the lock usually follows.
| Door | What it normally carries |
|---|---|
| Timber, external | A mortice lock, often with a nightlatch |
| uPVC or composite | A euro cylinder in a multipoint strip |
| Aluminium or metal | A multipoint or a cylinder-operated lock case |
| Timber, internal | A lighter mortice latch or sashlock |
| Older timber door or outbuilding | Sometimes a surface-mounted rim lock |
Two exceptions break the pattern. Newer timber doors can be built with multipoints, so age often tells you more than material. A flat entrance door onto a shared corridor has its own considerations, since the method of exit is part of what suits it and a lock opening from inside without a key may come under a different standard.
What to Settle Before a Replacement
Identification narrows the problem but does not confirm the faulty part or its replacement, because similar-looking locks differ in size, operation, security specification and compatibility. Ask four questions: what is fitted; what is causing the fault, given that a stiff key or loose handle may come from the cylinder, case, gearbox, spindle or alignment; whether one part or an adjustment would do; and whether the replacement will fit, work reliably and secure that entrance. Broad labels such as "euro cylinder" or "five-lever sashlock" cannot pin down a part. Brand names and anti-snap labels prove no standard, which belongs to a specific product. If lock changes follow lost keys, a move or a break-in, key control and damage matter as well as fit. When in doubt, arrange an inspection before buying; a clear diagnosis can prevent an unnecessary full lock change.
Types You Meet Less Often
Other Types on UK Doors Most of the locks below are fitted in addition to a main lock rather than replacing it.
| Type | What it is |
|---|---|
| Door bolt | Surface-mounted and hand-operated, adding a second fixing point |
| Hinge bolt | Fitted on the hinge side to resist that side being forced |
| Push-button lock | A coded mechanical lock with no batteries, wiring or app |
| Patio door lock | A sliding-door arrangement in the handle or the panel edge |
| Window lock | A separate family with its own fittings |
Push-button locks are common on offices, storage rooms, shared areas and some residential side entrances. A numbered keypad on the outside pairs with a knob, lever or thumbturn inside, and the correct code releases the handle to operate the latch or lock case. The keypad may connect to a separate tubular latch, mortice latch or case, so it is not always the full lock.
Sliding patio door locks differ from those on hinged doors. Built into the handle assembly or linked to a mechanism in the panel's vertical edge, they can use one hook or bolt, multiple hooks, a key cylinder, a handle with a thumbturn, an anti-lift device and keeps on the meeting frame or fixed panel. Check the handle shape, fixing positions, cylinder profile and faceplate, and photograph the hooks or bolts.
The table at the head of the page covers the rest.
Unsure What You Have? Ask Us
Still Not Sure? Ask Us Tell us about the door and we will say what lock is fitted, what it would take to change or repair it, and what that costs before we start.
It helps to know the door material and where the keyhole sits, and to have a photo of the faceplate along the edge while the door is open. If the door cannot currently be locked or secured, say so straight away.
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Door Lock Type Questions
How can I tell what type of door lock I have?
First establish the door's material, then decide whether the lock occupies a recess in its edge or rests on its surface. For identification, consider the keyhole and faceplate alongside any handles and the number of locking positions. Those clues distinguish a cylinder or multipoint mechanism from a nightlatch or mortice lock. A key moves a deadlock's bolt, with no handle latch. Sashlocks pair a spring latch with a deadbolt, normally needing handles and a keyhole.
What type of lock is usually fitted to a uPVC door?
Multipoint locking is the common arrangement for modern uPVC entrance doors. The wider assembly includes a locking strip, hooks, gearbox and frame keeps. A euro cylinder operates it together with the handles, so the cylinder is only part of the system being identified.
How do I know if I have a mortice lock or a nightlatch?
Use the casing's location to tell them apart: inside the edge means a mortice lock, while a visible body fixed to the inner face indicates a nightlatch. Either discovery is only part of the check, because a timber entrance door may carry both.
Is a euro cylinder the same as a multipoint lock?
The distinction is between a component and a mechanism: the key operates a euro cylinder, whereas multipoint locking extends along the edge. Installing a replacement cylinder changes only that item. Neither the handles nor the gearbox, locking strip or locking points are replaced by that work.
Can I replace the cylinder without replacing the complete door lock?
The cylinder is often replaceable as a separate part when the mechanism around it is compatible and in working order. Assess any fault before choosing that work. Changing this component will leave problems from a damaged gearbox, poor door alignment or handle wear unresolved.
Can I identify a door lock from the key alone?
Full identification is usually not possible from just a key. Branding and shape may point to a particular mechanism or cylinder, but the complete model, dimensions and security standard seldom follow from that alone. Clear views of the door edge and visible markings provide better clues.
What if there is no brand name visible on the lock?
Use the lock's physical details if no maker's name is visible: its shape, size, operation and locking-point positions may identify it. Include the door edge, handles, frame keeps and keyhole in photographs. Write down any symbols or numbers rather than dismissing them as unrelated markings.
Does a five-lever lock automatically meet BS 3621?
Five-lever construction does not automatically establish compliance with BS 3621; it describes internal workings. Check the exact model, visible full standard reference, certification marking and original documents. Compliant locks normally reference BS 3621 on the product or packaging, often beside a certification mark. Earlier editions may appear on older locks; the current edition is BS 3621:2017+A1:2024. This performance standard addresses tested, thief-resistant mechanical single-point assemblies needing a key for locking and unlocking on both sides. Lever quantity, a long bolt and familiar branding prove nothing alone. Keyless opening from inside may involve another standard, as BS 3621 requires keyed exit.
How can I tell whether my door has a deadlock or a sashlock?
A deadlock has a bolt worked by a key and no handle-operated latch; a sashlock adds a spring latch to its deadbolt, normally with handles and a keyhole. For a wider check, establish the door material first, then whether the lock is inset into the edge or surface-mounted. Handles, keyhole, faceplate and locking-point count help distinguish mortice, nightlatch, cylinder and multipoint arrangements.
Why does my lock work when the door is open but not when it is closed?
Often, closing the door reveals an alignment problem: multipoint locking points, a bolt or a latch are missing the frame keeps. The next check should cover movement in the door, hinge wear and poor alignment. Establish those points before assuming the lock has to be replaced.
Can a locksmith identify my lock from photographs?
Yes, photographs can often reveal the type of lock and may point towards its manufacturer or model. Choosing an exactly compatible part can require more information, though. For mortice cases and multipoint gearboxes in particular, measurements or an inspection may still be necessary.
What should I do if the door is locked and I cannot identify the lock?
Do not respond to an unknown lock by drilling, prising or forcing the key or handle repeatedly. Pause further work on the locked door and seek a qualified locksmith's help with identification. Ask for advice on proceeding once the fitting has been identified.