What is BS3621?
BS 3621 is the British Standard for thief-resistant key-operated locks, typically the five-lever mortice deadlock on a wooden door, or a deadlocking nightlatch. Locks that meet it have been tested against attacks such as drilling, picking and forcing.
You can usually spot one by the Kitemark and “BS 3621” stamped on the faceplate on the edge of the door.
Which doors does it apply to?
BS3621 is mainly about locks on traditional timber doors, common on the period and interwar houses found across Harrow, Pinner and north-west London. Most uPVC and composite doors use a multipoint lock with a euro cylinder, and insurers generally look at the security of the cylinder and door instead. Wording varies between policies, so always check yours.
uPVC and composite doors: what to look for
- TS007 3-star: a Kitemarked anti-snap cylinder (or a 1-star cylinder with 2-star security handles).
- Sold Secure Diamond (SS312): an independent standard that tests cylinders against the attack methods used in real break-ins, including lock snapping.
- PAS 24: a standard for the whole door set, common on newer doors.
Lock snapping is one of the most common ways burglars get through uPVC doors with standard cylinders, so upgrading the cylinder is one of the best-value security improvements you can make.
How to check your own doors
- Timber doors: look on the edge of the door for “BS 3621” and a Kitemark.
- uPVC and composite doors: look at the cylinder face around the keyhole for a Kitemark with stars, or a Sold Secure Diamond mark.
- Read your policy’s security section for the exact wording, especially for “final exit doors”.
- If in doubt, send a photo on WhatsApp and we will tell you what you have.
Upgrading
A standard lock replacement is typically £90-120, and anti-snap cylinders vary by size and rating. Tested products are matched to your door, and the exact product and price are agreed with you before fitting. After a burglary, ask your insurer what they require before replacing locks.
Common questions
Does my insurer really check?
Insurers typically check lock standards when there is a burglary claim, particularly if there are no signs of forced entry. It is worth making sure your locks match the policy wording before you need to claim.
Is a 3-star cylinder better than Sold Secure Diamond?
Both are strong anti-snap standards tested in different ways, and many high-security cylinders carry both. Either is a big step up from a standard unrated cylinder.
Can you tell me if my locks meet the standard?
Yes. Send a photo of the lock or cylinder on WhatsApp, or it can be checked during any visit.