BS3621 Locks: What Your Home Insurer Actually Requires
Buried in the small print of most UK home insurance policies is a clause about your locks. Get it wrong and a burglary claim can be reduced or refused. The standard you will see referenced most often is BS3621. Here is what it means in plain English and how to check whether your doors comply.
What is BS3621?
BS3621 is the British Standard for thief-resistant locks. A lock that carries it has been independently tested to resist common attacks — picking, drilling and forced entry — for a defined period. The current standard requires a lock that can be locked and unlocked by key from both inside and outside, which is why it is the benchmark for final exit doors. When a lock passes, it carries the British Standard kitemark: a heart-shaped symbol, usually stamped on the faceplate or the lock body, alongside the number BS3621.
Why insurers care
Insurers price risk. A door secured to BS3621 is significantly harder to defeat, so most policies make it a condition of cover for external doors. If your policy says "final exit doors must be fitted with a lock conforming to BS3621" and yours is not, the insurer may argue you breached the terms. Reading your own policy wording is the only reliable way to know what is expected of you.
BS3621, BS8621 and BS10621 — what's the difference?
- BS3621 — key-locking from both sides. The standard final exit door lock.
- BS8621 — keyless egress: you can always leave by turning a thumbturn from the inside without a key. Important for fire escape, flats and houses in multiple occupation where people need to get out fast.
- BS10621 — allows the door to be "locked down" externally so the internal thumbturn is overridden, used in specific commercial settings.
For a typical house, BS3621 covers most doors, but if a door is the only escape route, BS8621 may be the safer and more appropriate choice. A locksmith can advise on the right balance of security and escape for each door.
How to check your own locks
- Open the door and look at the lock's faceplate (the metal strip on the edge of the door).
- Look for the kitemark heart symbol and the text BS3621.
- On a mortice lock, count the levers — insurers generally want a 5-lever mechanism, and BS3621 units are 5-lever.
- If there is no kitemark, assume the lock does not meet the standard.
What about uPVC and composite doors?
Multipoint locks on uPVC and composite doors are tested under different European standards rather than BS3621, which was written with timber doors in mind. For these doors, insurers usually focus on the cylinder — an anti-snap, TS007 3-star or SS312 Diamond cylinder is the key upgrade. If your multipoint mechanism is failing or the door is hard to lock, our guide to uPVC repairs covers gearbox and alignment issues that often get mistaken for lock faults.
Bringing a door up to standard
Upgrading a non-compliant timber door usually means fitting a BS3621 5-lever mortice deadlock, which a locksmith can do in a single visit. Our overview of lock replacement and installation explains how the right standard is matched to each door and how the work is carried out without damaging the door.
The takeaway
BS3621 is not red tape — it is a genuinely tougher lock and the line most insurers draw between covered and not covered. Spend ten minutes checking your faceplates for the kitemark, read your policy's lock clause, and put right anything that falls short. It is far cheaper than a refused claim.