Window Lock Key Replacement UK: Types, Identification & What to Do

If you have lost a window lock key, identify the lock type first - espagnolette, cockspur, fitch or key-operated sash - then either order a brand-matched replacement online or call a locksmith to cut a key to the lock or replace the unit. Replacement keys bought online typically cost £4-£10; City Locksmith London rekeys window locks from £55 and changes a lock from £69 labour, both excluding VAT. It is worth doing promptly: a window was the entry point in around 20% of domestic burglaries where the offender got in, and a forced window lock or catch accounted for around 7% on its own (ONS, Crime Survey for England and Wales, Nature of Crime: burglary, Table 3b, year ending March 2025).

Why Does a Missing Window Lock Key Matter?

Windows are the second most common point of entry for burglars in England and Wales. In the year ending March 2025, offenders who got into a home came in through a window in around 20% of incidents, against around 77% through a door (ONS, Crime Survey for England and Wales, Nature of Crime: burglary, Table 3b).

The detail inside that 20% is the useful part. Around 7% of all entries involved forcing a window lock or catch and around 5% involved a window that was open or could simply be pushed open, so the hardware and how it is used both matter. Note also that the survey sample for these tables is small, so treat the split as an indication of pattern rather than a precise measurement.

A missing or damaged window lock key leaves you unable to lock the window at all, and the problem is especially common after moving into a new home where previous occupants took or lost the keys.

Knowing which lock type you have - and the fastest route to a replacement key - is an essential part of keeping your home secure. This guide covers every common UK window lock type, how to identify each one, and what to do when a key is lost or a lock fails.

For a broader look at door and window security, see our guide to security door and window lock types in London.

What Are the Main Types of Window Lock in the UK?

UK windows use four principal lock types. Identifying yours correctly is the critical first step before ordering any replacement key.

Lock type	Era / window type	Key feature to spot	Key measurement needed
Espagnolette (espag)	1990s-present, uPVC casement	Square spindle at base; 2 fixing screws	Spindle length (15-60 mm), backset
Cockspur	Pre-late 1990s; uPVC, timber, aluminium	Curved spur/tongue; 4 screws in square pattern	Backset/step height; left or right-handed
Fitch fastener	Traditional timber sash windows	Pivoting cam-action catch at meeting rails	Cam projection; screw centres
Key-operated sash lock	Victorian/Edwardian sash; modern secure models	Visible keyhole in handle or frame	Key profile; lock brand

Espagnolette (Espag) Locks - the Most Common Type

Espagnolette locks are the standard on virtually all uPVC casement windows installed in Britain since the 1990s. The handle turns a square spindle (usually 7 mm) that drives a multipoint locking gearbox running along the edge of the window frame, securing the sash at several points simultaneously.

How to identify an espag lock:

• Square spindle protruding from the base of the handle
• Two fixing screws aligned vertically with the handle
• Handle turns to engage multiple locking points around the frame

What you need to measure for a replacement key or handle:

• Spindle length from base of handle to tip (common sizes: 15, 20, 25, 30, 35, 40, 43, 50, 60 mm)
• Backset - the distance from the spindle centre to the window edge
• Whether the handle is inline (universal) or cranked (left or right-handed)

Espag keys are brand-specific. Check the back of the handle or the gearbox body for a manufacturer name (common UK brands include ERA, Mila, Avocet, Securistyle, Yale).

Cockspur Handles - Older uPVC and Timber Windows

Cockspur handles are found on uPVC windows made before the late 1990s and on many timber and aluminium-framed windows. Instead of a spindle-driven gearbox, the security relies on a curved spur (the “cockspur”) pressing down against a wedge keep on the opposite frame.

How to identify a cockspur handle:

• Distinctive curved spur or tongue projecting from the handle body
• Four fixing screws arranged in a roughly square pattern (approximately 24 mm x 32 mm centres)
• Locking versions have a key button integrated into the handle

What you need for a replacement:

• Backset height - from the base of the handle down to the underside of the spur
• Handedness - left-handed or right-handed (the spur faces opposite directions)

One important security note: cockspur handles are single-point only. They pre-date the PAS 24 era and cannot be brought up to that standard by changing the handle alone, because PAS 24 tests the whole window. If your property still has original cockspur handles on accessible ground-floor windows, moving to a modern multipoint espag system is a meaningful upgrade rather than a cosmetic one. Our residential locksmith service can advise on the options.

Fitch Fasteners - Traditional Sash Windows

Fitch fasteners (also called fitch catches) are the traditional lock on timber sliding sash windows, which are common in Victorian and Edwardian properties across London. They work as a pivoting cam that draws the two sashes together at the meeting rail.

How to identify a fitch fastener:

• Pivoting oval or teardrop-shaped catch mounted on the inner sash
• No spindle - the cam rotates to lock the meeting rails together
• Lockable versions have a small keyhole in the cam body

Fitch fasteners are not high-security on their own. For ground-floor or accessible sash windows, a secondary sash stop or key-locking bolt provides a meaningful upgrade.

Key-Operated Window Locks

Separate key-operated locks - bolt-through locks, frame bolts, and handle locks with an integral keyhole - can be fitted to any window type. They are common on PAS 24-rated windows and on ground-floor casements where additional security is specified.

Replacement keys for these locks require either the key code stamped on the lock body or a locksmith to cut a new key to the lock directly.

What Security Standard Should a UK Window Meet?

There is one standard that matters and one building regulation that decides when it applies.

• PAS 24 is the enhanced security performance standard for doorsets and windows in the UK. It replaced the old window standard BS 7950:1997, which was withdrawn when PAS 24:2012 was published. The current edition is PAS 24:2022 (+A1:2024). It is a whole-product test: frame, sash, glazing, hardware and fixings are attacked together, so a PAS 24 window cannot be assembled from separately “secure” parts.
• Approved Document Q (Security - Dwellings) has applied in England since October 2015. It requires easily accessible windows and doors in new dwellings, including those created by a material change of use, to be made to a design proven by test to PAS 24 or an equivalent. “Easily accessible” broadly means at ground or basement level, above a low-pitched roof, or within about 2 metres of the ground or an access balcony.

The catch most homeowners are not told: Approved Document Q does not apply when you replace a window in an existing home. If you are having windows replaced, PAS 24 certification is something you have to ask for, not something you get by default. Products certified under a Secured by Design member scheme are accepted as meeting Document Q.

How to Identify Your Window Lock Without a Key

If you have lost the key and are unsure of the lock type:

1. Look at the handle base. A square spindle = espag. A curved tongue = cockspur. A visible keyhole = key-operated lock.
2. Count the fixing screws. Two screws in line = almost certainly espag. Four screws in a square = cockspur.
3. Check for brand markings. Look on the back of the handle (use a small mirror), on the gearbox body visible at the window edge, or on the keep plate on the frame.
4. Note the window material and age. uPVC post-1995 = almost always espag. Timber sash = fitch or key-operated. Older uPVC or aluminium = likely cockspur.
5. Photograph everything. A clear photo of the handle front, the lock body, and any visible text lets a locksmith or online supplier identify the model in minutes.

How Do You Get a Replacement Window Lock Key?

Option 1: Order Online From a Specialist Supplier

Once you have identified the brand and model, replacement window keys are available from specialist UK window-hardware suppliers for around £4-£10. Several will identify the correct key from a clear photo you email them, which saves guessing at a model number.

This route works well when:

• You can clearly identify the brand and model
• At least one window of that type is still accessible and unlocked
• The lock itself is in good working order

Option 2: Call a Locksmith to Cut a Key to the Lock

A locksmith can cut a replacement key without the original by picking or manipulating the lock and then impressioning or cutting a new blank to match. This is the best option when no replacement key is available online or the lock model is discontinued.

At City Locksmith London we carry a wide range of window lock key blanks and can cut keys on-site across all London postcodes. Contact us for a free quote.

Iulian H., lead locksmith at City Locksmith London, says: “We open a locked window non-destructively wherever we can and confirm the price before we start, because replacing a whole espag gearbox is often avoidable.”

Option 3: Rekey the Lock

If you want to change which key operates the lock - for example, after moving into a new property - a locksmith can rekey it so that only new keys will work. Window lock rekeying starts from £55 with City Locksmith London.

Option 4: Replace the Entire Lock Unit

If the lock is corroded, seized, discontinued, or simply old and single-point, a full replacement is often the most practical and cost-effective solution. Like-for-like lock change labour starts from £69, and upgrading an older cockspur to a modern multipoint espag system significantly improves your home security.

For a full breakdown of what to expect on cost, see our locksmith price list.

What if the Window Is Locked Shut and You Cannot Open It?

If a window is stuck closed because the lock has jammed or the key is lost:

1. Do not force it. Forcing a jammed espag gearbox can crack the uPVC frame.
2. Apply lubricant. Silicone-based spray or graphite powder into the keyway can free a stiff mechanism.
3. Try a flathead screwdriver in the keyway - on simple cam-type locks this sometimes turns the cam, but avoid it on precision espag gearboxes.
4. Call a locksmith. A professional can open the window without damage in most cases, then replace or rekey the lock on the same visit.

City Locksmith London responds across Greater London within 25 minutes, 24 hours a day, 7 days a week. Request help now.

Common Problems That Cause Window Lock Key Issues

• Lost or misplaced keys - particularly common after moving into a new property where previous owners took all window keys
• Corrosion and rust - especially on older metal locks or external-facing hardware exposed to moisture
• Jammed mechanisms - caused by debris, paint build-up, or worn gearbox components inside espag systems
• Broken keys - snapped off in the lock due to wear, forcing or cold weather making metal brittle
• Discontinued models - older window lock ranges where replacement keys are no longer manufactured

Enhancing Window Security Beyond the Lock

Replacing or finding a matching key restores baseline security, but consider these additional measures for ground-floor and accessible windows:

• Secondary sash stops - limit how far a casement or sash window can be pushed open from outside
• Window security film - applied to the glass, it holds shattered panes together and slows entry
• Chain locks - allow ventilation while preventing the window opening enough to climb through
• Smart window sensors - alert you when a window is opened unexpectedly

For a full overview of window security options, see our guide to security door and window lock types.

When Should You Call a Professional Locksmith?

DIY key replacement works when the lock is accessible, in good condition, and the correct key is available online. Call a professional when:

• The window is locked closed and you cannot access it
• The lock mechanism is seized, damaged, or corroded
• No matching replacement key exists for a discontinued model
• You want the security reassurance of a lock change with a new keyed system
• You are moving into a property and want all window locks rekeyed to a single new key

City Locksmith London operates 24/7, covers all London postcodes with a 25-minute response time, charges no call-out fee, and uses fully insured, DBS-checked engineers. Our residential locksmith team handles all window lock types - espag, cockspur, fitch, and key-operated - across the full range of uPVC, timber, and aluminium windows.

Get a free quote from City Locksmith London