LOCK STANDARDS • INSURANCE
What is a BS3621 lock?
BS3621 is a British Standard for thief-resistant locks that can be locked by key from both sides. A lock meeting it carries a kitemark and the number stamped on the faceplate on the edge of the door. Many home insurance policies specify it for final-exit doors, though the wording varies between insurers.
How to tell whether you already have one
Open the door and look at the metal faceplate running along its edge, where the bolt comes out. A lock that meets the standard has the kitemark — a heart-shaped symbol — and the text BS3621 stamped into that plate, usually with a year.
If there is no marking, the lock does not meet the standard, whatever it looks like and however solid it feels. The key is not a reliable guide either: plenty of five-lever-looking keys belong to locks that were never tested to it.
This takes about ten seconds per door and is worth doing before you need to know.
The family of standards, briefly
| Standard | What it is | Typical use |
|---|---|---|
| BS3621 | Key-locking from both inside and outside | Final-exit doors where everyone has a key |
| BS8621 | Keyless exit from inside, key from outside | Flats and HMOs, where escape must not need a key |
| BS10621 | Keyless exit normally, lockable from outside when empty | Premises locked up and left, such as shops |
The important point is that these are not better-and-worse versions of one another. They are different answers to a different question about how people get out. Fitting BS3621 to a flat door that needs keyless escape is a fire-safety problem, not an upgrade.
What insurers actually ask for
Many home policies specify a five-lever mortice deadlock to BS3621 on final-exit doors, and key-lockable locks on accessible windows. Some go further and specify locks on patio and French doors. Some say nothing specific at all.
Read your own policy wording. "Insurance-approved" is a phrase used in advertising and it has no fixed meaning; what has meaning is the sentence in your policy document. If it names BS3621, fitting a lock that meets it is inexpensive next to arguing about a claim. If it does not, you may still want one, but nobody should be selling it to you on the basis that your insurer demands it when they have not read your policy either.
A second point worth knowing: some policies require the locks to have been in use, not merely fitted. Leaving a BS3621 deadlock unlocked because the nightlatch is quicker can matter.
What fitting one involves
On a timber door that already has a mortice lock of the same case size, the new lock goes into the existing mortice and the job is straightforward. A different case depth or backset means enlarging the mortice and adjusting the keep in the frame.
Old doors are rarely square, so the keep position usually needs adjusting for the bolt to throw fully. A bolt that engages only part way looks locked and resists very little, which is one of the more common things we find on doors that have never been checked.
BS3621 locks are for timber doors. uPVC and composite doors use a multipoint mechanism operated by a euro cylinder, and the equivalent question there is whether the cylinder is anti-snap — a different standard entirely.
What it costs
A mortice lock or deadlock supplied and fitted is listed from £156, normally with three keys, and that covers a standard replacement into an existing mortice. Enlarging a mortice or replacing a damaged keep takes longer. Call-out and labour are charged separately at the published rates.
For a uPVC or composite door, the comparable work is a cylinder replacement from £120, where the relevant question is the anti-snap rating rather than BS3621.
Common questions
Does my insurance require a BS3621 lock?
It may. Many policies specify one for final-exit doors, but not all do, and the wording differs between insurers. Read your own policy document rather than relying on general advice or on what a locksmith tells you about your cover.
How do I know if my lock is BS3621?
Look at the faceplate on the edge of the door. A lock meeting the standard has the kitemark and BS3621 stamped on it. No marking means no standard, regardless of how the lock looks or how many levers the key appears to have.
What is the difference between a sashlock and a deadlock?
A sashlock has both a latch and a bolt, so it holds the door shut and locks it. A deadlock has a bolt only and is used alongside a nightlatch. Both are available to BS3621; which you need depends on what else is on the door.
Can a BS3621 lock be fitted to a uPVC door?
No. BS3621 locks are mortice locks for timber doors. A uPVC or composite door has a multipoint mechanism and a euro cylinder, and the equivalent upgrade there is an anti-snap cylinder to TS007 three star or Sold Secure Diamond.
Is a BS3621 lock enough on its own?
No lock is. It raises the time and noise required and it satisfies a common policy condition, which are both worth having. It does not make a door impenetrable, and anyone telling you otherwise is selling rather than explaining.
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