How to Tell If Your Lock Is BS3621
A BS3621 lock carries the British Standards kitemark stamped on the lock faceplate, usually with the number 3621 beside it. Check the forend of your mortice lock or the face of the cylinder — no kitemark, no certification. Many insurers require it on final exit doors. Unsure? Call 07984 547185 and we will identify what you have.
BS3621 is the number that appears in home insurance small print across Britain: the British Standard for thief-resistant locks. Insurers like it because it is testable — a lock either meets the standard or it does not, and the kitemark proves which.
But most homeowners have never checked. This guide shows you where to look, what the markings mean, and what to do if your locks fall short.
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Where to find the kitemark
Open the door and look at the lock's faceplate — the metal strip on the door edge. A BS3621 mortice lock stamps the British Standards kitemark there (the heart-and-torch symbol) along with the number 3621. On euro cylinders, check the cylinder face for the kitemark and any TS007 stars.
The marking must be on the lock itself, not the packaging it came in and not the locksmith's invoice. If you cannot find it, assume it is not certified.
What BS3621 actually tests
The standard covers resistance to picking, drilling and forced entry for mortice and cylinder locks on external doors. It also requires a minimum bolt throw — 20mm for mortice deadlocks — and anti-pick features. It is a genuine security bar, not a paperwork exercise.
Note the scope: BS3621 covers the lock. The door, frame and fitting still matter — a certified lock in a rotten frame is theatre, not security.
What if your locks are not BS3621?
First, check your insurance wording — many policies require it on final exit doors, and a claim after a break-in can be affected. Then get the locks assessed: sometimes a serviceable non-BS lock can stay on an internal door while the external doors get upgraded.
Upgrading to BS3621 mortice locks on timber doors is standard work — see our lock replacement page. For cylinders, the TS007 route in our anti-snap guide covers the equivalent. Or just ring 07984 547185 and we will tell you what you have.
Frequently asked questions
What does BS3621 mean?
It is the British Standard for thief-resistant locks, covering resistance to picking, drilling and force, with a 20mm minimum bolt throw for mortice deadlocks. The kitemark on the lock faceplate proves certification.
Where is the BS3621 kitemark?
On the lock faceplate — the metal strip on the door edge — showing the heart-and-torch kitemark with the number 3621. On cylinders, check the cylinder face. No marking on the lock itself means no certification.
Do I legally need BS3621 locks?
Not by law, but most home insurance policies require them on final exit doors as a policy condition. Check your wording — a break-in claim can be affected if the locks do not meet the stated standard.
Is BS3621 the same as anti-snap?
Related but different. BS3621 is the mortice lock standard; anti-snap cylinders are rated under TS007. A timber door wants BS3621; a uPVC door with a euro cylinder wants TS007 stars. Some doors benefit from both approaches.
Can you upgrade my locks to BS3621?
Yes. BS3621 mortice upgrades on timber doors are routine work — measured, fitted and tested in one visit, with the kitemark visible on the new lock. Call 07984 547185 for a quote.