Mortice Sash LockFitting & Repair South London
The lock that carries your front, back and side timber doors: handle to open, key to secure, one case, one strike. We supply, fit, repair and upgrade 3-lever and 5-lever BS3621 sash locks across every CR, SW, SE, SM and BR postcode — typically on site within 30 minutes.
Fixed prices · No VAT · No call-out fee
The lock that carries the daily use of a British timber door.
A mortice sash lock is the workhorse sitting inside the edge of most wooden UK doors. One metal case buried in the stile, two jobs: a sprung latch that moves when you press the handle and keeps the door closed, and a deadbolt that throws into the frame when you turn the key. That simple combination is why sash locks live on front doors, back doors, utility doors, garage personnel doors and almost every solid timber internal door fitted before 1990.
The difference between a sash lock and a mortice deadlock comes down to that latch. A deadlock has no handle and no latch — it is pure security, usually paired with a night latch on a Victorian front door. A sashlock on its own can be a final-exit lock, provided it is a 5-lever BS3621 Kitemarked model. We fit both every day and carry 5 lever BS3621 stock and 3 lever internal stock on every van across South London.
This page covers every decision a homeowner, landlord or tenant needs to make: which lever count suits the door, what size case to buy, how BS3621 relates to your home insurance, what the common failure points look like and what it costs us to fit or upgrade one. If you just want the job booked, the quickest path is the phone — skim the contact page or read about us first if you want to know who is turning up. For the wider lock and security library see our locksmith advice blog.
Sashlock vs Deadlock — which one is actually on your door?
These get mixed up in every second phone call we take. One has a handle and a key, one has only a key. The choice decides which lock you can legally use on a final-exit door under UK building regulations and your home insurance wording.
Mortice Sash Lock
Latch and bolt in one case. The handle lets you open and close the door without a key; the key only comes out when you want it locked. Works on almost any timber door — front, back, internal, garage personnel, stockroom.
- Handle opens the door — no key needed to enter or exit
- 5-lever BS3621 version is a valid final-exit lock on its own
- Fits timber doors with a stile thick enough for a 64mm+ case
- 3-lever version suitable for internal and low-risk back doors
Mortice Deadlock
Key only, no handle and no latch. Used as the second lock on a Victorian or Edwardian front door, paired with a night latch above it. It cannot open the door by itself — the night latch handles daily use.
- No handle cut-out needed — smaller door pocket required
- Fewer moving parts — fewer things to go wrong long-term
- Standard UK night latch + deadlock combo seen on period doors
- 5-lever version meets BS3621 when paired with compliant night latch
3-lever or 5-lever? The answer is whatever your insurer will accept.
Every mortice sash lock is graded by the number of levers in the mechanism — each lever is a small brass flag the key has to lift into position before the bolt can move. Lever count is the closest shorthand British homeowners have to "how secure is this lock", but the real question is whether it carries a BS3621 Kitemark. Here is how the two common grades compare in plain numbers.
| Feature | 3-Lever Sashlock | 5-Lever Sashlock (BS3621) |
|---|---|---|
| Lever differs (key patterns) | Around 400 | Minimum 1,000 — often 10,000+ on premium brands |
| BS3621 Kitemark | Not eligible | Yes, when Kitemark stamped |
| Accepted for final-exit door | No | Yes — meets most UK insurer wording |
| Anti-drill / anti-pick features | Basic | Hardened plates, anti-pick curtain, anti-saw bolt |
| Case depth options | 64mm / 76mm | 64mm / 76mm / 102mm |
| Typical use | Internal doors, sheds, garden gates, low-risk back doors | Front doors, back doors, ground-floor final-exit doors |
| Replacement cost (fitted) | from £180 | from £180 |
When a 3-lever sashlock is fine
Internal doors — bedroom, study, utility, office. Sheds and outbuildings that are not insured contents locations. Back doors where there is already a BS3621 lock elsewhere on the same door. A 3-lever lock still stops casual opportunists and gives a sensible level of privacy, but it is not what insurers mean when they write "5-lever mortice deadlock conforming to BS3621" in your policy.
When 5-lever BS3621 is mandatory
Final-exit front, back and side doors on any insured home. Tenancies regulated under the Housing Act where landlords have a duty to provide a secure front door. If your policy says the word Kitemark or BS3621, a 3-lever sashlock voids that clause — in practice insurers have refused theft claims where the fitted lock did not match. Our free audit tells you in 10 minutes. See our BS3621 + insurance guide for the exact wording.
Nine parts of a mortice sash lock — and why each one matters when it fails.
Understanding the anatomy helps you diagnose the fault over the phone. Nine times out of ten, when a homeowner says "the lock is sticking" it is one specific part — not the whole lock — that needs replacing. Here is every component inside the case that we see on a typical service call.
Lock Case
The steel rectangular box buried in the door edge. Houses every moving part. Size determines backset and which handle position will line up with the spindle.
Faceplate
The narrow brass or satin-nickel strip you see at the door edge, screwed into the mortice pocket. Shows the maker, model and — on a compliant lock — the BS3621 Kitemark stamp.
Sprung Latch (Bevel)
The angled tongue that clicks shut when the door closes. Pulled back when the handle is pressed. Wears on its leading edge after 10–15 years of slamming.
Deadbolt
The squared-off steel bar that throws into the strike when you turn the key. On BS3621 locks the bolt contains hardened anti-saw pins to resist a hacksaw.
Lever Pack
Three or five stamped-brass levers stacked inside the case. The correct key lifts each lever to a precise height; any wrong lift stops the bolt moving. More levers = more combinations = more security.
Anti-Pick Curtain
Only found on BS3621 5-lever locks. A rotating shield inside the keyhole that stops lock picks reaching the levers at the correct angle. This is what stops a standard pick kit.
Follower (Spindle Hub)
Square hole in the middle of the case that the door handle's spindle passes through. Retracts the latch when the handle is turned. A loose follower is why handles feel "sloppy" over time.
Keyway (Keyhole)
The escutcheon-lined slot on the face of the door. BS3621 locks use a stepped profile that will not accept thin pick tools or bump keys.
Box Keep & Strike
The receiving plate on the frame. A flat strike is cheaper; a proper box keep — a deep steel pocket screwed to the frame stud — more than doubles resistance to a kick attack.
Measure the case depth before you buy — or send us one photo and stop guessing.
A mortice sash lock only fits the pocket already cut in your door. Buy the wrong size and you will be staring at a gap, a splintered stile or a strike that will not line up. The two numbers that matter are case depth (how far into the door the lock sits) and backset (the distance from the door edge to the keyhole centre).
Narrow-Stile Sash
Backset 44mm. Used on slim-stile timber doors and many back doors. The compact size leaves less wood to compromise on a 32mm stile, but gives a shorter bolt throw. Check stile thickness is at least 44mm before ordering.
Standard UK Sash
Backset 57mm. The most common fitted size on post-1980 hardwood front and back doors. Bolt throw of 14mm. Every major brand (Union, ERA, Yale, Chubb) stocks a 76mm 5-lever BS3621 model at this size.
Heavy-Duty Sash
Backset 82mm. Used on period doors with thick Victorian stiles and on modern insurance-rated hardwood doors. Longer bolt, heavier case, more room for hardened internal components. Harder to find off-the-shelf — we carry stock.
Not sure which size you need?
Send one photo of the faceplate (the brass strip on the door edge) plus one of the key to our WhatsApp line. We will confirm the make, model, lever count and size within minutes — and tell you exactly what a like-for-like swap will cost. No hard sell, no visit needed for a quote.
Send Photo on WhatsApp- DepthFaceplate to back of case
- BacksetDoor edge to keyhole centre
- HeightFaceplate top-to-bottom
- BoltHow far the deadbolt throws
- HandleCentre of spindle to centre of key
The six faults we see on mortice sash locks — and what each one actually needs.
Before you replace the whole lock, read this. Most sash lock problems are a single worn part or a frame alignment issue that takes 20 minutes to fix. A full lock change is the right call about a third of the time — the rest of the time we can repair or re-align for a lot less money.
Key turns but bolt will not throw
The levers lift but the bolt catches on the strike plate. Classic symptom of door drop: the bolt is reaching the frame 1–3mm below the strike hole.
Key stuck halfway, will not come out
Levers are worn or one has snapped. Forcing it risks breaking the bow clean off and leaving a half-key inside the case — a broken key extraction job at that point.
Handle droops or feels loose
The follower (spindle hub) inside the case is worn round. Handle flops, latch does not retract properly, door rattles. Common after 15+ years of heavy use.
Lock jammed shut, no key response
A lever spring has snapped or a foreign object is inside the keyway. Can happen on very old locks where the key has been forced for years.
Latch will not hold the door closed
The sprung latch has worn flat on the leading edge and no longer engages the strike. Door pushes open in the wind. Often paired with a new bright silver line on the faceplate.
Not BS3621 — insurance clause failing
Faceplate has no Kitemark stamp. Your policy requires one. Not a repair — this is the upgrade job where we swap to a 5-lever BS3621 case while keeping the same handles and escutcheons.
Four UK-made mortice sash locks that earn their spot — and why.
Every van carries the same four core models, plus a few specialist alternatives for narrow stiles and period doors. These are the locks we fit for our own families and for landlord portfolios that need to stand up to inspection.
Union StrongBOLT 2K75
5-Lever · BS3621 Kitemark · 76mm / 64mmThe default choice for most UK front and back doors. Hardened bolt pin, anti-pick curtain, 28mm box keep, 1,000 key differs. Made in Willenhall, Birmingham. Backed by a 10-year mechanical guarantee and spare parts readily available.
ERA Fortress 5-Lever
5-Lever · BS3621 · 76mm standardA popular insurer-approved lock with a reversible latch and a high-security anti-pick shield. Good value for landlords kitting out a portfolio; keyed-alike sets available so one key fits every unit's final-exit door.
Yale PM552 BS 5-Lever
5-Lever · BS3621 · 76mm caseThe Yale mortice sash lock you will find specified in new-build estates across South London. Nickel-plated steel bolt, anti-saw pins, hardened lever pack. Three-star cut key blanks stocked by most high-street retailers if you lose one.
Chubb 3G114E
5-Lever · BS3621 · 76mm / 102mmPremium British-made lock specified by insurers for higher-value properties. Detainer discs prevent pick manipulation, 10,000+ key differs, rare overnight-pick resistance. Expect a longer delivery lead time on the 102mm case — worth the wait for a period hardwood door.
Every burglary claim starts with one question: was the lock to BS3621?
South London insurers have refused more than a third of timber-door theft claims in the past three years on the same clause: the lock on the final-exit door did not carry a Kitemark. A compliant 5-lever mortice sash lock is the cheapest insurance-rated upgrade you can make to a wooden front door — lower cost than replacing the door itself, lower cost than a new alarm. The numbers opposite are what we see across South London jobs every week.
Four services that handle 99% of the sash lock calls we take.
Whether you are halfway through replacing a handle and need someone to finish safely, or the lock has refused to open at 11pm on a Sunday, one of these four is almost certainly what you need. Fixed pricing, same-day attendance across every South London postcode.
Supply & Fit
BS3621 5-lever mortice sash lock supplied, fitted, chiselled flush to the faceplate, strike aligned, two keys cut. Takes 45–60 minutes on a typical timber door.
Repair & Realign
Strike plate re-alignment, loose follower tightening, lever spring replacement where serviceable. Saves you a full lock change when the case is still sound.
BS3621 Upgrade
Like-for-like 3-lever to 5-lever Kitemark swap to meet your home insurance clause. Handles, escutcheons and finish stay identical — only the lock case changes.
Emergency Open-Up
Locked out and the sash lock has seized, jammed or the key has snapped. Non-destructive picking where possible; replacement lock fitted same visit if needed.
Three steps between you ringing and the new lock turning smoothly.
Call or WhatsApp
One line, no script. Tell us the door type, whether the key still works and roughly what went wrong. If you can send a photo of the faceplate we will confirm the size before anyone gets in a van. Fixed quote given on the phone — no "we'll see when we arrive".
≈ 5 minutes30-Minute Arrival
A DBS-checked engineer turns up in a marked, insured van with the correct 5-lever BS3621 stock, a replacement strike plate, a handful of cylinder options and a power drill for the rare drill-out job. ID card shown at the door before anything else.
Across CR/SW/SE/SM/BRFitted, Tested, Guaranteed
New lock fitted, chiselled flush, strike aligned, door tested both directions, keys cut, old lock taken away for recycling. Written invoice with a 12-month workmanship guarantee. Card or cash accepted on completion.
Typically 45 minThe small things that turn a lock fit into a proper job.
We are not the cheapest van in South London and we never promise to be. What we are is the one you call back for the next door — because nothing we fit has had to be revisited.
BS3621 Kitemark Stock On Every Van
Union, ERA, Yale, Chubb — we don't nip off to the wholesaler mid-job. Fitted from van stock, keys cut on site.
DBS-Checked Engineers Only
Every engineer background checked and uniformed. ID shown before anyone crosses your threshold.
Fixed Price, No VAT on Top
Quote stays quote. If the job needs extra parts, you agree the cost before we cut into the door — never after.
30-Minute Typical Response
Average arrival time across the SW, SE, CR, SM and BR postcodes. Night jobs the same — we staff 24/7.
No-Damage Promise
Non-destructive entry first. If a lock has to come out, we cover the cost of a matching replacement case.
12-Month Workmanship Guarantee
Fit, alignment and key cut all covered. If the lock fails for a reason we caused, we come back free.
Free Insurance Compliance Audit
We check every lock on the door and tell you plainly whether your policy wording is satisfied — no pressure, no upsell.
Written Invoice & Certificate
Paper trail for your insurer and landlord. BS3621 upgrade jobs come with a dated compliance certificate.
Every South London Postcode Covered
From Croydon and Sutton to Norbury, Kenley, Sanderstead, Purley, Coulsdon and every street in between.
Card & Cash Accepted
Card, cash — paid on completion, never upfront. No deposits, no holding fees.
Fixed mortice sash lock pricing — no call-out fee, no VAT on top.
Every figure below is the starting price for a standard South London residential job during business hours. After-midnight and bank-holiday rates are quoted separately on the phone — we will tell you before we dispatch.
Sash Lockout
- Non-destructive pick first
- 24/7 cover
- No call-out fee
5-Lever Supply & Fit
- Kitemark stock, 2 keys cut
- Strike realignment included
- Compliance certificate
- 12-month guarantee
Broken Key Extraction
- Specialist extractor tools
- Lock survives where possible
- Key blank cut on site
Sashlock + Night Latch
- Classic Victorian front door
- Two BS locks, one visit
- 4 keys cut
What homeowners say after a mortice sash lock visit.
Insurance renewal flagged our old 3-lever sashlock. Lloyd turned up with the Kitemark paperwork in an unmarked folder, fitted a Union BS3621 to the same pocket, and emailed the certificate before he left. No drama. Policy re-priced cheaper.
Tried to swap the sashlock myself — ended up with a chiselled-out mess and a stuck key. They answered the WhatsApp at 8.40pm, came round, got the door open without damage and fitted a proper 5-lever the same evening. Solid work.
I manage six flats in SM6 and every final-exit door needed an insurer-friendly sash lock. They keyed-alike four of them so my tenants each have one key for their own flat and I have a master for access. Quick, clean, invoiced properly.
The questions people actually ask on the phone.
What is a mortice sash lock?
A mortice sash lock is a lock fitted inside the edge of a timber door that combines a sprung latch (operated by the handle) and a deadbolt (operated by the key) in a single steel case. The handle lets you open and close the door without a key; the key only has to come out when you want it locked shut. Sashlocks sit in almost every wooden front door, back door, utility door and solid internal door across the UK.
What is the difference between a mortice sash lock and a mortice deadlock?
A sashlock has a handle-operated latch plus a keyed deadbolt, so it can be used on any door that needs day-to-day handle opening. A deadlock only has the keyed bolt — no handle, no latch. Deadlocks are used as a second lock on period front doors, usually paired with a night latch that handles the daily opening.
Do I need a 3-lever or a 5-lever mortice sash lock?
Internal doors and low-risk back doors can use a 3-lever sashlock. Any external final-exit door should use a 5-lever BS3621 Kitemarked sashlock, because that is what UK home insurers ask for in the policy small print. 3-lever locks are not BS3621 compliant — fitting one on the front door of an insured home will usually void the theft cover on a claim. See our BS3621 and insurance guide for the exact wording.
What size mortice sash lock do I need?
Measure the existing case depth — from the faceplate at the door edge to the back of the lock case. The two common UK sizes are 64mm (with a 44mm backset, for narrow stile doors) and 76mm (with a 57mm backset, the default on most modern UK doors). Period doors sometimes use a 102mm case with an 82mm backset. If you are not sure, send a photo of the faceplate to our WhatsApp and we will identify it for you in minutes.
How much does a mortice sash lock cost to replace in South London?
A BS3621 5-lever mortice sash lock fitting starts from £180 including the lock, labour, two cut keys and strike plate re-alignment. A like-for-like 3-lever swap is the same starting price. Emergency lockout or broken-key extraction on a sash lock starts at £120. We quote a fixed figure on the phone before we dispatch — no call-out fee, no VAT on top.
Is every mortice sash lock BS3621 approved?
No. Only 5-lever models that carry the British Standards Institution Kitemark and BS3621:2007 stamp are insurance approved. 3-lever sashlocks are not eligible for BS3621 certification — they are classified for internal doors and low-risk outbuildings only. Always check the lock faceplate for the Kitemark shield and the BS3621 number before assuming a lock meets your policy wording.
Can I replace a mortice sash lock myself?
If the new lock matches the old case size, backset and strike position exactly, a confident DIYer can do it in under an hour. The risk is that most replacement sashlocks do not match the old pocket down to the millimetre — the case depth will differ by 3–5mm, the backset will be out, or the new strike will sit below the old mortice. At that point the door edge needs chiselling, which is where most DIY jobs go wrong and end up as a locksmith callout anyway. A mortice specialist will fit a like-for-like in 45 minutes with no damage.
How long does a BS3621 mortice sash lock last?
A properly fitted 5-lever BS3621 sashlock from Union, ERA, Yale or Chubb will last 15–25 years before the follower wears or a lever spring gives up. The weakest point is usually the sprung latch, which flattens on its leading edge after tens of thousands of slams. Periodically lubricating the keyway with graphite and making sure the door is not dropping on its hinges will add years to the working life.
Related lock types, repairs and location coverage.
A mortice sash lock is rarely the only security on a South London front door. If you are upgrading or need more than one item on the same visit, the links below cover the full range of related work we do.
Explore the site
Related locks & problems
South London locations we cover
Mortice sash lock fitted today across South London.
BS3621 Kitemark stock on every van. Fixed prices from £180. No call-out fee, no VAT, 12-month guarantee on every fit. Pick up the phone or send one photo on WhatsApp — the quote lands back before you finish a cup of tea.
24/7 emergency locksmith serving South London since 2015 — trusted by homeowners, landlords and businesses across Sutton, Mitcham, Wallington, Cheam, Purley and surrounding areas.