Sash Window Locks
Fitted Across South London
Heritage-safe, insurance-approved sash window locks fitted by locksmiths who know timber windows — from period Victorian boxes in Dulwich to Georgian front rooms in Clapham. Dual screws, Fitch upgrades, sash stops and keyed fasteners — priced, fitted, tested.
Fixed prices · No VAT · No call-out fee
Sash Windows Deserve the Right Lock — Not a Generic One
A well-made sash window is one of the most attractive features in a South London home — and one of the easiest to leave exposed. The original Victorian or Georgian fastener sitting on your meeting rail was designed to hold the sashes snug against draught. Most of them never had a keyhole. That is exactly why roughly nine in ten UK home insurers now insist on a key-operated window lock on every sash that can be reached from the ground, a porch roof, a boundary wall or a drainpipe.
We fit sash window locks across the whole of South London — Victorian terraces in Clapham and Battersea, Edwardian semis in Streatham and Balham, Georgian front rooms in Greenwich and Dulwich, Bay-fronted bedsits in Croydon and Sutton. Every property is different, and the lock that works on a two-over-two Georgian sash will not always fit a six-over-six Victorian box. You can see the full list of areas we cover across South London on our coverage page.
This page is the practical version of the conversation we would have on your doorstep. We cover the seven common sash lock types, how each one holds up against a forced entry, which satisfy a typical home-contents policy, how we fit them without splitting original timber, and what it actually costs. If you would rather read a plain-English breakdown of other lock types first, our locksmith advice blog has longer guides on British Standard locks, anti-snap cylinders and wooden door hardware.
Straight answer: If you want a single lock that makes a sash window pass almost every UK home insurance policy, fit a keyed dual screw through both meeting rails. Add a sash stop upstairs so windows can be left open safely for ventilation. We carry both on the van and fit them from £180 per window.
Most calls we take about sash locks come from two groups of people. The first is new homeowners who have just received their insurance schedule, spotted the line about "all accessible windows must have key-operated locks", and realised their pretty brass Fitch fastener will not satisfy the wording. The second is parents — a child opens a first-floor sash, a neighbour calls it in, and a safe ventilation solution suddenly moves to the top of the list. Both problems are solved with the same toolkit, fitted the same afternoon. You can read a little about who we are and how we work, or send us photos of your window for a fixed quote before we arrive.
Seven Sash Window Locks — Which One Does Your Window Need?
Traditional fasteners, keyed upgrades, sash stops and bolts. Every lock below does a different job — and only some will pass a British home insurance check. Here is the plain-English breakdown before you choose.
Keyed Dual Screw
A threaded barrel sits inside the lower meeting rail, and a long keyed bolt screws through into the upper rail. Nothing visible on the outside, almost impossible to force from the sash gap. This is the lock insurers ask for.
Insurance approvedFitch Fastener (Locking)
The classic half-moon lever seen on thousands of South London sashes — now available in a keyed version. The lever pulls the sashes together for a tight seal and the key locks the throw in place. Heritage-friendly, brass or chrome.
Keyed version passesBrighton Sash Fastener
A thumb-screw threads through both meeting rails and tightens them together. The locking pattern has a concealed screw head that needs a T-bar key. Strong pull-together action — excellent for warped or slightly sprung timber sashes.
Locking pattern passesQuadrant Arm Fastener
A curved arm swings from the upper sash into a keep plate on the lower sash. Simple, mechanical, original to a lot of Victorian boxes. In its non-keyed form it holds the sash shut but will not satisfy an insurance clause on its own.
Pair with a dual screwSash Stop (Ventilation Lock)
A short brass peg drilled into the upper sash that blocks the lower sash from travelling past a fixed point — typically 100mm. Turn the key and the peg retracts so the window opens fully. Ideal for bedrooms, nurseries and bathrooms.
Child-safe & policy-friendlySash Bolt (Through-Bolt)
A brass sleeve drilled into the lower rail, with a long threaded bolt that passes through into the upper sash. Powerful hold but needs the meeting rails to be in perfect alignment — we level the sashes first on older boxes.
Insurance approvedClaw Fastener (Non-Keyed)
A pivoting metal claw that drops into a keep — period-correct on a lot of 19th-century boxes. It will hold the sash snug against draught but offers almost no resistance against a forced entry. We keep them on the window for look, add a real lock behind them.
Not insurance compliantWill Your Sash Lock Pass an Insurance Check?
British home-contents policies share broadly the same window-lock wording. Here is the policy language in plain English, and the British Standard that ties into it for windows.
What the policy says
Nearly every UK home-contents policy carries a line along these lines: "all external doors must be fitted with a five-lever mortice lock to BS3621 or a multi-point locking system, and all accessible windows must be fitted with key-operated window locks."
The word that matters is accessible. Insurers interpret it broadly — any window a reasonably athletic person could climb into without a ladder. That includes ground-floor sashes, first-floor sashes over a porch or bay, windows near a flat roof, gutter or drainpipe, and rear sashes over a wall or shed.
- All ground-floor windows — sash or casement, front and back.
- Any window over a flat roof — kitchen extensions, garage roofs, bin stores.
- Windows on porch or bay roofs — classic entry point on South London terraces.
- Any sash reachable by drainpipe or boundary wall — some insurers explicitly include these.
The British Standard angle
For windows the relevant standard is BS7950 — Specification for enhanced security performance of casement and tilt/turn windows for domestic applications. It tests forced entry resistance, glazing security and lock strength. On timber sashes BS7950 usually applies to the whole window unit rather than a single add-on lock, so for retrofit fitting we follow the spirit of the standard: keyed, steel-bolt resistance, anti-drill where possible.
For doors the familiar standard is BS3621 — covered in depth on our BS3621 locks page. A full insurance-compliant home usually pairs BS3621 door locks with keyed BS7950-spirit window locks on every accessible sash.
- Locks must be key-operated, not simple push or turn fasteners.
- Both meeting rails must be physically joined when locked, not just held by a latch.
- Keys must be removable when locked — a key left in the window fails most clauses.
- Always check your own schedule — cover varies by property, postcode and insurer.
From Fasten to Fully Locked — The Mechanism in Plain English
The keyed dual screw is the gold-standard insurance-compliant sash lock — here is how the mechanism actually holds two sashes together when a key is turned.
Threaded barrel in the lower rail
We drill a clean pilot hole into the lower meeting rail and press-fit a brass threaded sleeve. The sleeve is the part that actually carries the load — not the timber.
Keep plate into the upper rail
A matching brass plate sits flush into the upper meeting rail, aligned on exactly the same axis. This catches the bolt when it travels across the rail gap.
Keyed bolt threads through
A hardened steel bolt screws through the lower sleeve and crosses into the upper keep. Because it is a screw thread — not a latch — it cannot be pushed back with a blade or wire.
Key removes, sashes are locked
The key un-threads from the bolt head and comes away clean. Both sashes are now physically joined by a steel shaft buried inside the rails. The window cannot slide in either direction.
Second dual screw on the other side
For most sash widths over 900mm we fit a second dual screw on the opposite side of the meeting rails. Two bolts stops any attempt to twist the sashes apart by force.
The bolt crosses both meeting rails. Nothing visible from outside. No wire or blade can retract it — it must be unscrewed with the key.
Sash Window Lock Services Across South London
Supply, fit, repair and replace — four fixed-price services covering every sash window scenario from a single bedroom lock to a full Victorian four-storey refit.
Supply & Fit Insurance-Approved Locks
Keyed dual screws, locking Fitch fasteners, Brighton patterns and sash bolts — supplied, drilled, fitted, tested on the day. Brass, chrome or black finishes on request.
From £180 per windowRepair & Realign Existing Locks
Old sash bolt sticking? Dual screw threads stripped? We strip-down painted-over fasteners, re-thread barrels, re-align meeting rails so the bolt travels smoothly again.
From £180Sash Stops for Ventilation
Child-safe sash stops fitted in 15 minutes per window. Window opens to a safe gap (100mm) for airflow, key-retracts for full opening when you need it. Ideal for nurseries and bathrooms.
From £180 fittedMulti-Window Insurance Upgrade
Whole-property upgrade to satisfy a new insurance schedule — every accessible sash brought up to keyed spec in a single visit. Send photos on WhatsApp for a fixed quote.
Photo-based quoteIs a Sash Window Lock the Right Call for You?
Two checklists — one covers the situations where a sash lock is almost always the right answer, the other covers cases where you may want a different product entirely.
Fit a sash lock if…
- You have original timber sash windows — Georgian, Victorian or Edwardian — and the fastener on the meeting rail does not have a keyhole.
- A new insurance schedule mentions key-operated window locks and your policy start date is close.
- Your children's bedrooms have sash windows and you need to lock them to a safe ventilation gap.
- You have sashes over a porch roof, flat roof or bay — the classic accessible-window scenario insurers flag.
- You are letting the property — landlords almost always need keyed window locks on accessible sashes to satisfy tenancy and insurance.
- The original fasteners are painted over, seized, or missing — fit new keyed replacements and keep the heritage look.
Consider an alternative if…
- You have uPVC casement windows — those use espagnolette or multi-point locks instead. See our main window locks page.
- Your sashes are on the third floor or higher with no flat roof below — some insurers don't require locks at that height, though we still recommend them.
- The sashes are badly rotten or the cords have gone — we will still fit a lock, but a sash restoration will save more trouble longer term.
- You rent the property and the landlord hasn't agreed to any drilling — we can't drill into sashes without the owner's permission.
- The property is Grade I listed and your Listed Building Officer hasn't yet signed off on added hardware.
Sash Lock, Fitted in Three Visits Most People Remember
From the first call to a fully fitted, insurance-approved sash window — here is what a typical job with us looks like.
Send us photos on WhatsApp
Snap the window, the existing fastener and the meeting rail. We price the lock, confirm the right product for your timber and send a fixed quote back within the hour — no surveys, no call-out fee.
We arrive with everything needed
Our van carries keyed dual screws, Fitch fasteners, Brighton patterns, sash stops and sash bolts — brass, chrome and satin finishes. Nothing is ordered in afterwards. Most jobs are drilled, fitted and tested inside the hour.
Tested & signed off
We demonstrate the lock on the sash you watched us fit, talk you through the key, and leave a short written note for your insurance records. 12-month workmanship guarantee starts the moment we leave.
The South London Locksmith That Actually Knows Sash Windows
Most locksmiths treat every window like a uPVC unit. Sashes are different — timber moves, cords drift, paint locks rails. These are the reasons South London owners book with us.
Heritage-Trained Locksmiths
We have worked on Georgian sashes in Greenwich and Edwardian sashes in Streatham since 2015. Your original joinery is the priority.
DBS-Checked Engineers
Every locksmith on the team carries a current enhanced DBS certificate — safe around children, elderly relatives and tenants.
30-Min Response Across South London
Croydon, Sutton, Wallington, Clapham, Balham, Streatham, Dulwich — our fleet is always within half an hour.
Fixed Prices, No VAT, No Call-Out Fee
You pay the price we quote on WhatsApp. Never any hidden extras, surveys, ladder charges or evening surcharges before midnight.
Brass, Chrome or Black Finishes
We carry Fitch, Brighton, dual screw and sash stop hardware in three finishes — so the new lock matches the original fastener.
12-Month Workmanship Guarantee
If a lock sticks, misaligns or rattles within a year we come back and fix it — parts and labour included, same-day where possible.
Plain-English Insurance Advice
We read the wording on your policy schedule and quote the exact product that satisfies it — no up-sell to locks you don't actually need.
Card or Cash Accepted
Pay however suits you on the day — card reader on the van, cash welcome. Card, cash, or bank transfer accepted, no surcharge for any method.
Sash Window Lock Fitting Costs in South London
Fixed prices confirmed on WhatsApp before we arrive. No VAT, no call-out fee, no ladder surcharge, no pressure up-sells. Prices below are per window — multi-window jobs get a photo-based fixed quote.
Fitch / Brighton Fastener
Heritage keyed fastener, brass or chrome, drilled into meeting rail.
- Lock & labour included
- Brass or chrome finish
- Insurance-compliant
- 12-month guarantee
Keyed Dual Screw
Through-rail steel bolt, invisible from outside, insurance-grade.
- Hidden bolt — no exterior hardware
- Chubb / Yale quality
- Original fastener stays in place
- Insurance schedule note included
Sash Stop (Ventilation)
Safe-gap brass peg — child safe, key retracts for full opening.
- Safe ventilation gap (100mm)
- Child-safe on first-floor sashes
- Keyed lock/unlock
- Ideal for nurseries
Whole-House Upgrade
Every accessible sash brought to insurance spec in one visit.
- Send photos on WhatsApp
- Fixed price — no surveys
- Single visit, single invoice
- Landlord-ready receipts
Complex or bespoke sashes — send photos on WhatsApp for a fixed quote. After midnight — prices increase, call or WhatsApp for an exact quote.
South London Sash Owners Who Booked With Us
Real reviews from real properties — Victorian conversions, Georgian townhouses, Edwardian semis. Every one of them a sash window job.
"Our Victorian terrace came with original Fitch fasteners that our new insurer wouldn't accept. The team fitted keyed dual screws on six sashes in one afternoon — the brass matched the original hardware perfectly. Sent me a written note to attach to the policy. Proper professionals."
"Needed sash stops for the kids' bedroom — first-floor sashes over a porch roof. Arrived same morning, drilled both windows in 20 minutes, showed my partner how the keys worked, left the place tidy. Better service than we got from our boiler company, frankly."
"Our sash bolt had seized from twenty years of paint — thought we'd have to replace the whole fastener. Engineer stripped it down, re-threaded the barrel, tested twice, charged the quoted fixed price. No drama, no up-sell. I'd book them again for any window in the house."
From Georgian terraces to Victorian bay-fronted semis — we fit sash window locks that respect the original timber and pass every major UK insurance policy.
When Old Locks Stop Doing Their Job
Six faults we see every week across South London — with the honest cause and the fix that actually works on heritage timber sashes.
The Fitch won't turn
A century of gloss has bonded the lever to its plate. Forcing it will crack the lever or rip the fixings clean out of the rail. This is the most common call we get in Victorian properties.
Dual screw won't cross the gap
When the sashes sit at different heights the keyed bolt catches against the upper rail instead of dropping into its keep. Usual cause — a broken sash cord or a cord box that's come loose.
The key spins but nothing tightens
Years of over-tightening strips the brass thread in the barrel or the bolt itself. The key turns, the bolt stays where it is, the lock is effectively open.
We have the lock but not the key
Keys for dual screws, Brighton patterns and sash bolts are small, distinctive, and easy to lose. Hardware stores don't usually stock replacements.
Gap between the rails is too wide
Old timber sashes swell and shrink with the seasons. If the meeting rails have drifted apart more than a few millimetres, a dual screw won't bridge the gap and a Fitch will rattle.
Insurer says "these don't count"
Traditional non-keyed Fitch, claw or quadrant fasteners satisfy the window mechanically but fail a policy check on the key-operated clause. Renewal gets refused or premiums jump.
Heritage-first locksmithing
Securing a Listed Sash Without Damaging the Joinery
South London has some of the finest period housing stock in the country — Georgian runs in Greenwich and Blackheath, early Victorian villas in Dulwich, Arts & Crafts semis in Streatham Hill, and conservation areas in pockets of almost every borough. A lot of these properties are listed Grade II, and almost all of them came with non-keyed Fitch or claw fasteners that now fall short of modern insurance.
The good news — most sash window lock upgrades are legally classed as like-for-like reversible hardware changes, which means they usually do not require planning or listed building consent. That said, always confirm with your Listed Building Officer before any drilling. We have worked with listed properties across South London for over a decade and we know where to place — and where not to place — a new lock on original joinery.
- Brass hardware in period finish — polished, aged or un-lacquered to match existing.
- Pilot-drilled, paint-sealed holes — all drill dust captured, no mess.
- Original fasteners left in place — we fit alongside, not instead.
- Reversible fittings — surface-mounted sash stops on Grade II sashes.
- Conservation-area friendly — no bright plating on street-facing sashes.
- Written records on request — for listed building compliance.
Sash Window Lock Questions, Answered Plainly
Everything we get asked on the doorstep before a fitting — condensed.
Do I need a key-operated lock on my sash windows for insurance?
Around 90% of UK home insurance policies require key-operated window locks on all accessible windows — that includes sash windows on the ground floor, first floor, or anywhere reachable from a flat roof, porch or drainpipe. A traditional non-locking Fitch fastener on its own will usually fail the policy wording, so insurers ask for a dual screw, keyed sash lock or sash stop alongside it.
The word your policy will use is usually "accessible", and insurers interpret it broadly. If in doubt, upgrade — an £180 fitting today costs far less than a rejected claim.
What is the best lock for a sash window?
The most secure everyday choice is a keyed dual screw (such as the Chubb/Yale 8013) fitted through both meeting rails — it passes insurance checks, works on timber windows of any age, and leaves the original heritage fastener in place. For ventilation locking, pair it with a sash stop.
If you want an insurance-compliant lock that also looks period-correct on the outside of the sash, a locking Fitch fastener in brass is an excellent alternative — especially in conservation areas.
How much does it cost to fit sash window locks in South London?
Sash window lock fitting starts from £180 per window at Locksmith South London — that covers supply and fitting of a keyed lock, paint-safe drilling and a security check. Multi-window jobs get a fixed quote — send photos on WhatsApp and we'll price the full job in one go.
See our full lock replacement cost page for how sash locks compare to door lock work.
Can you fit sash window locks to a listed building?
Yes. We use surface-mounted or discreetly drilled locks that don't alter the original joinery — brass finishes are matched to the existing fastener where possible. Always check with your listed building officer before any permanent alteration, but most keyed sash locks qualify as reversible security upgrades.
We can provide written specs for your listed-building officer if required.
Will a sash lock damage my original window?
Not when fitted by a sash-experienced locksmith. We pre-drill at the correct angle, cap exposed holes with brass sleeves, and test the meeting rail alignment before and after fitting. Soft timber, painted-over sashes and cord-balanced boxes all need different handling — we work around them instead of forcing the lock.
If a sash is badly warped or rotten, we will tell you rather than drill into it — a damaged sash needs restoration before it is ready for new hardware.
Can you secure a sash window open for ventilation?
Yes — sash stops are the right product. A brass peg fits into the upper sash and blocks the lower sash from travelling past a safe ventilation gap (usually 100mm). Remove the stop with the key to open the window fully. It's the standard child-safe and warm-weather solution for bedrooms and bathrooms.
How many sash locks do I need per window?
On sashes wider than around 900mm we recommend two locks — one on each side of the meeting rails. Narrower sashes (cottage-sized or cloakroom windows) can get away with one central lock. Insurance-wise, the policy wording usually says "locked" — not "how many" — so one well-placed keyed lock satisfies the clause on most smaller sashes.
Are sash window locks the same as window restrictors?
Not quite. A sash lock holds the two sashes together so the window cannot slide open at all. A sash stop or window restrictor limits how far the window can open — useful for ventilation, child safety, and for some listed-property policies that require limited-opening hardware. Most homes end up with both, fitted together.
Pair Your Sash Lock With These
Windows are only one side of the insurance picture. Most South London homeowners pair a sash window upgrade with one of these — check the full list below.
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Heritage-Safe, Insurance-Approved Sash Locks — Fitted Today
Fixed prices from £180 per window. DBS-checked engineers. 12-month guarantee. Call now for free advice, or WhatsApp us photos of your windows for a same-day fixed quote.
24/7 emergency locksmith serving South London since 2015 — trusted by homeowners, landlords and businesses across Sutton, Mitcham, Wallington, Cheam, Purley and surrounding areas.