What BS3621 covers, in short
A BS3621 lock is a mortice deadlock or nightlatch that an independent body has tested against a British Standard. The tests cover resistance to picking, drilling and forced attack. The lock carries a kitemark stamp on the faceplate as proof, because the stamp shows it passed.
Many insurers specify this standard for external doors, which is why people call it an insurance-approved lock. Your policy wording decides what your insurer needs. A mobile locksmith covering Bayswater and nearby W2 districts fits and checks BS3621 locks. You get the price confirmed before any work starts.
Mortice deadlocks and nightlatches
BS3621 covers two common lock types. A mortice deadlock sits inside the door edge, and you work it with a key from both sides. It resists attack well when the door is fully locked. For that reason, it is the standard fitting for most solid timber front and back doors.
A BS3621 nightlatch is a deadlocking, surface-mounted lock with a separate cylinder. Not every nightlatch meets it, so look for the kitemark. It is useful where the door is too thin for a mortice case. Some designs also pair with a mortice deadlock. This gives a two-lock setup on a final exit door, which many insurers prefer.
Which one suits you depends on the door itself. We look at its thickness, the existing cut-outs, and whether you want a deadbolt alongside a self-latching action. We confirm this on inspection, because a phone call is not enough to judge it.
Why London flats need this checked
Many London flats and period conversions have had their locks changed several times, since tenants, landlords and previous owners each add their own. It is common to find a lock that looks the part but carries no kitemark stamp at all.
A BS3621 stamp is the only reliable proof of the standard, since looks and price prove nothing. Checking the faceplate with the door open takes a minute. Do it at move-in, at a tenancy changeover or at a policy renewal, because even well-kept flats often have this gap.
Fitting and checking service
The service covers checking an existing lock against the standard. It also covers supplying and fitting a new BS3621 mortice deadlock or nightlatch while you upgrade. For a full swap that includes this upgrade, see the lock change page.
If your door is uPVC or composite and not timber, consider an anti-snap euro cylinder as well. BS3621 applies to lock assemblies such as mortice deadlocks and some nightlatches, not to euro cylinders, so we check the two separately. To see how cylinder ratings work, read our guide to anti-snap cylinder ratings.
Smart locks and period doors
Some people want a smart lock on an older door. Our guide to fitting a smart lock on a period door covers the options. However, check your insurer’s lock standard before you change a final exit door, because policies differ.
After a break-in or a failed lock
A break-in, or a lock that has failed outright, is a natural point to check the standard, because a like-for-like swap of a non-BS3621 lock can leave a policy unmet even after the door is secure again. The burglary repair page covers same-day security after a forced entry, including this check.
Check or upgrade your lock
To find out whether your lock meets BS3621, or to have an insurance-approved lock fitted, get in touch. Request a call back or send your details through the contact form. A mobile locksmith covering Bayswater and nearby W2 districts will confirm what you need and the price before any work starts.