Window & Door Security Locks: BS 3621, Multi-Point Locking & PAS 24 Standard

Summary

Domestic security hardware is a surprisingly technical area. Insurance requirements, standards compliance, and the interaction between the lock and the door/window frame all affect whether a lock provides genuine security or merely the appearance of it. A five-lever deadlock in a weak timber frame provides little more protection than a cheap rim lock.

For locksmiths, joiners, and door installers, understanding BS 3621, PAS 24, and the Secured by Design (SBD) scheme ensures customers get the right protection and their insurance remains valid. For carpenters fitting timber doors and frames, understanding fixing requirements and strike plate specification prevents locks failing at the frame rather than the lock body.

Key Facts

• BS 3621:2020 — the key British Standard for key-operated deadlocks; specifies: anti-drill, anti-pick, anti-bump protection; minimum 1000 key combinations; deadlocking bolt; tested to 1000 locking cycles; insurance standard minimum
• BS 3621 markings — locks should be marked on the body or packaging with "BS 3621 Kitemark" and the BSI Kitemark logo; fake or misrepresented claims are common in cheaper locks
• Five-lever deadlock — traditional mortice deadlock; five levers provide the required minimum key combinations under BS 3621; morticed into the door edge; the bolt shoots into a box strike in the frame
• Multi-point locking system (MLS) — modern PVCu and composite door standard; one handle/thumb-turn operation drops or lifts a central cam that simultaneously drives multiple bolts: top, bottom, and side latch/deadbolts; MLS with hook bolts is significantly harder to attack than a single deadlock
• PAS 24:2022 — specification for enhanced security for doors and windows; used in Secured by Design (police-approved) schemes and social housing; tests include: dynamic loading (forcing attack), static load, soft body impact, lock manipulation; requires both door and hardware to be tested as a system
• Secured by Design (SBD) — UK Police initiative; uses PAS 24 and other standards; Secured by Design accreditation requires a product be tested and certified as a system (door + frame + hardware together, not just the lock)
• BS 7950 — Enhanced security performance requirements for hinged, pivoted or sliding windows; older standard; superseded in part by PAS 24 for complete window sets but still referenced in insurance documents
• Window restrictors — required in any window above 2m from ground level where a child could reach; restrictor limits opening to 100mm; must not require a tool to release in an emergency (but can require deliberate effort)
• Night latch (Yale lock) — spring latch, not a deadlock; not BS 3621; insurance typically requires a deadlock in addition to a night latch; snib feature (deadlocking the latch from inside) does not substitute for a BS 3621 deadlock
• Euro profile cylinder — the cylinder used in most modern PVCu door systems; anti-snap cylinders (TS007 3-star, or 1-star door + 2-star cylinder combination) recommended to resist lock snapping (a common burglary technique); never replace a composite door cylinder with a cheap non-snap-resistant grade
• Hinge security — door security depends on hinges as much as locks; external doors should use security hinges (hinge bolts or anti-jemmy features); minimum 3 hinges; BSEN 1935 Grade 11 or BS 7352 Grade 13 for external domestic
• Strike plate — the box strike (for mortice locks) or keep (for multi-point locking) must be strongly fixed to the frame with minimum 3" (75mm) screws into solid wood or masonry behind the frame; a weak strike is the most common failure point

Quick Reference Table

Detailed Guidance

BS 3621 — What It Actually Specifies

BS 3621:2020 is the current version. A lock meeting this standard must:

1. Deadlocking bolt — the bolt must lock in the extended (thrown) position; it cannot be retracted with a credit card or by pushing; the bolt engages the frame only when the key is turned
2. Anti-drill plates — hardened steel inserts in the lock body to prevent drilling through to the mechanism
3. Anti-pick — the lever mechanism resists manipulation by pick tools
4. Anti-bump — the mechanism resists bump key attacks (a common burglary technique using an impact force on a specially cut key)
5. Minimum 1000 key combinations — reduces the chance of accidental cross-keying; does not prevent determined picking
6. Tested cycle life — lock must operate 1,000 cycles without failure

Mortice vs rim: BS 3621 specifies mortice locks (fitted into the door edge) primarily. Rim locks (surface-mounted, such as Yale patterns) are available in BS 3621 specification but are less common and less robust for an exposed timber door edge.

Fitting quality matters: A BS 3621 lock poorly fitted (shallow mortice, thin door, weak frame) will not perform as tested. The door edge mortice depth must suit the lock; the door stile must be solid (not hollow near the lock); the frame must be sound.

Euro Cylinders and Lock Snapping

Lock snapping has been a significant residential burglary technique since the mid-2000s. The attacker uses a small tool (screwdriver, grips) to snap the cylinder at its weakest point (usually where the euro profile reduces in diameter behind the cam). Once snapped, the lock can be opened in seconds with a flat tool.

Anti-snap cylinders (TS007):

• TS007 is the technical specification for anti-snap performance
• A 3-star (★★★) cylinder provides full anti-snap, anti-drill, and anti-pick protection
• A 1-star door + 2-star cylinder combination also achieves the equivalent 3-star total

Key features of anti-snap cylinders:

• A sacrificial break point ahead of the cam (the cylinder snaps at this point deliberately, but the cam remains protected and cannot be operated without the key)
• Hardened steel elements around the critical mechanism
• Look for the TS007 logo and star rating on the packaging

Recommendation: Always replace any standard cylinder on an external PVCu or composite door with a TS007 3-star or equivalent anti-snap cylinder. The cost difference (£15–30 vs £5–15) is trivial compared to the security improvement.

Multi-Point Locking Systems

Most modern PVCu, composite, and aluminium doors use a multi-point locking system (MLS). The mechanism is operated by a handle or thumb-turn which drives a central gearbox, which in turn actuates multiple locking points:

• Hook bolts — shoot out horizontally and engage in a keep/strike in the frame; designed to resist jemmy/lever attacks
• Top and bottom rods — extend vertically into the door frame head and threshold
• Dead latch (centre) — spring-loaded latch for day-to-day use; anti-slam spring latch returns to open when handle pressed

Maintenance: MLS systems require periodic lubrication (graphite or petroleum jelly on latch bolts and hook bolts; avoid WD40 which attracts dirt); misalignment of the door (common in timber doors that swell seasonally) causes the bolts to bind and fail.

Replacement: When replacing an MLS, match the handing (left or right hand), backset (distance from edge to centreline of cylinder), and height between hook bolt centres to the existing keep/strike positions in the frame. Most PVCu door manufacturers publish their MLS specifications; the gearbox and trim must be compatible.

Strike Plate Fixing — The Critical Detail

The most common point of failure in domestic door lock attacks is not the lock itself but the frame around the strike plate. A standard boxed strike fixed with short screws into the thin timber frame section behind the PVCu casing will fail under a single shoulder charge.

Best practice for strike plate installation:

1. Use a box strike (deep keep) rather than a flat plate — box strikes engage the bolt or hook bolt into a deeper recess, making levering or pulling the frame apart harder
2. Use minimum 75mm (3") screws into the solid timber carcass or masonry behind the frame; short screws into the PVCu frame facing are inadequate
3. For timber doors: use security strike boxes (BS approved) or reinforced metal plates that spread the load over a larger area of the frame
4. For PVCu frames: ensure the composite timber reinforcement within the PVCu extrusion is solid at the strike position; some profiles have hollow sections — strike plates should be specified for the exact profile

Frequently Asked Questions

My customer has a PVCu door with a cheap cylinder. The house has been broken into before. What should I recommend?

Replace the cylinder with a TS007 3-star anti-snap cylinder of the correct profile (typically euro profile with the correct keying-alike requirement if other doors on the property need to match). Check that the multi-point lock has hook bolts (not just latches). Check that the strike keeps are well secured to solid timber behind the PVCu. Inspect hinges — PVCu door hinges with worn or missing anti-jemmy features should be replaced. The entire package costs £50–100 in materials and significantly reduces the break-in risk.

Does a BS 3621 deadlock on its own satisfy insurance requirements?

Usually yes for most standard UK home insurance policies, but always check with the customer's specific insurer. Some insurers also require window locks to meet BS 7950 or have key-operated locks; some require Secured by Design certification for new builds; some require night latches to also deadlock. The customer should call their insurer with the specific lock and window details if they are unsure.

Can I rekey an existing BS 3621 lock?

Yes — most locksmiths can rekey five-lever deadlocks. The levers inside the lock are changed to a new pattern matched to a new key. This is less expensive than replacement and maintains the BS 3621 certification. For euro cylinders, rekeying is not typically possible — replacement with a cylinder of the same profile is the standard approach.

Regulations & Standards

• BS 3621:2020 — Key-operated deadlocking locks; minimum insurance-grade specification

• PAS 24:2022 — Enhanced security performance for doors and windows used in construction

• TS007:2012 — Resistance to forced entry; cylinders; star ratings

• BS 7950:1995 — Enhanced security performance requirements for hinged and sliding windows

• Secured by Design — UK Police security scheme using PAS 24 and BS 3621 as minimum standards

• Secured by Design — Police-backed security scheme; approved products database

• Master Locksmith Association — Qualified locksmiths; standards guidance

• BSI: BS 3621 — Buy the standard from BSI

• draught proofing — Sealing external doors and windows

• lintel replacement — Structural work near door frames

• building regs overview — When window/door replacement requires notification

• handover documents — Certificates and documentation after lock installation