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

Quick Answer: Insurance companies require window and door locks to meet BS 3621 as a minimum for home insurance cover. BS 3621 specifies key-operated deadlocking for external doors. PAS 24:2022 is the enhanced security standard for doors and windows used in Secured by Design schemes. For window locks, insurers typically require either key-operated locks or British Standard window locks (BS 7950 for windows, BS EN 13126 for hardware). Always check with the customer's insurer before replacing locks — substituting a BS 3621 deadlock for a non-certified lock can invalidate insurance.

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

Quick Reference Table

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Lock Type Standard Security Level Typical Application
BS 3621 five-lever deadlock BS 3621:2020 Insurance minimum Timber external doors
Multi-point lock (hook bolts) BS 3621 or PAS 24 High PVCu, composite, timber doors
Anti-snap euro cylinder (TS007 3★) TS007:2012 High PVCu and composite doors
Standard euro cylinder None applicable Low — snap risk Do not use on external doors
Rim lock (night latch) — Low Internal use or supplementary only
Window lock (key operated) BS 7950 / BS EN 13126 Standard External windows
Child restrictor — Not security-rated Safety function
Door/Hardware Rating Description Use Case
PAS 24:2022 Enhanced security tested system Secured by Design; social housing; new build
SBD approval Police-backed security scheme New build, high-crime areas
BS 3621 lock only Minimum insurance standard Older property; timber door replacement
TS007 3-star cylinder Anti-snap cylinder Replacement cylinders in PVCu/composite doors
TS007 1★ door + 2★ cylinder Equivalent to 3-star total Flexible anti-snap specification

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):

Key features of anti-snap cylinders:

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:

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