BS3621 is the British Standard for thief-resistant door locks that need a key to operate from both sides. It is what most home insurers specify when they say a final exit door must have a conforming lock. The quickest check is to open the door, look at the narrow metal plate set into the door edge, and find the BSI Kitemark alongside the marking "BS3621".
Most people only come across the standard after a break-in or when an insurer questions a claim at renewal. This guide explains what the standard covers, how to read your lock's faceplate, what the related standards BS8621 and BS10621 mean, and why the question is different altogether if your door is uPVC or composite.
What BS3621 actually is
The current revision is BS 3621:2017+A1:2024, published by the British Standards Institution. It covers thief-resistant lock assemblies that use a key from both the inside and outside - what the standard calls "key egress". Locks tested to this revision have been independently assessed against drilling, picking, sawing and force.
Secured by Design, the police-backed crime prevention scheme, describes BS3621 as the minimum standard for locks on external or entrance doors. That is a useful benchmark: it does not mean every lock on every door must carry this certification, but it is where most insurer guidance and most security advice starts.
BS3621 is not a legal requirement. No legislation compels it. The obligation, where it exists, comes from your insurance policy, a tenancy agreement, or another contract - not a statute.
How to tell if your lock meets BS3621
Open the door and look at the faceplate - the narrow metal strip set into the door edge where the bolt sits. A certified lock will have the BSI Kitemark and the code "BS3621" stamped or engraved there. Both need to be present.
If the faceplate is painted or worn, clean it carefully before drawing any conclusions. If it is still unreadable, the lock's model number - sometimes visible on the body of the lock once the door is open - can be checked against the manufacturer's list of certified products.
"5 lever" on the faceplate is not the same thing
Five levers describes how a lock is built. BS3621 describes what a lock has been tested and certified to achieve. They are separate, and a lock can have five levers without ever being tested to BS3621.
This distinction matters because insurer guidance can blur it. Some policy wording asks for "a mortice deadlock with at least five levers", which leads people to assume any five-lever lock qualifies. It does not. The standard requires independent testing and certification beyond the lever count alone. Check for the Kitemark and the BS3621 stamp on the faceplate - not just the number of levers.
BS3621, BS8621 and BS10621 - which one your door needs
Three standards cover this product family:
| Standard | Inside operation | Key point |
|---|---|---|
| BS3621 | Key required from inside and outside | Standard for most external timber doors |
| BS8621 | Thumbturn (keyless egress) | Where occupants need to exit quickly without finding a key |
| BS10621 | Dual mode - keyless egress, plus a secure mode that deadlocks from outside | Must only be used where an alternative means of escape exists |
BS3621 is the right starting point for most external timber doors. BS8621 answers a different problem: getting out. Where a door is the escape route and hunting for a key would cost time, the thumbturn matters more than the second keyhole does, which is why flats and shared buildings often specify it.
BS10621 sits between the two. It gives you keyless egress in normal use, plus a secure mode that deadlocks the door from outside. Secured by Design is explicit that it must only be used on properties with another means of escape - if that door is the only way out, this is the wrong standard for it.
For rented properties and HMOs, the choice of standard has a direct bearing on tenants' safety and on compliance. We cover locks for rented property if you need to work through which variant is right for the people living there.
What your insurer actually requires
Most home insurers name BS3621 as the required standard for final exit doors - front, back, and any side door through which an occupant might leave the property. Allianz states that most insurers insist a lock conforms to BS3621, and that a claim can be refused where the lock that was beaten did not meet it.
The honest caveat is that policy wording varies. Some policies name BS3621 explicitly. Others describe "a mortice deadlock with at least five levers" and leave the certified standard implied rather than stated. A few accept one description as equivalent to the other; some do not. The only definitive check is your own policy document.
If you have recently had a break-in and are uncertain whether your locks met the required standard, we can advise on the door and carry out repairs after a break-in that bring it to the level your insurer needs. If there is any doubt about a current claim, speak to your insurer before you accept a settlement.
uPVC and composite doors - BS3621 probably is not your standard
BS3621 is a mortice lock standard. It applies to timber doors, where the lock body sits inside the door and a bolt throws into the frame. If your door is uPVC or composite, it almost certainly runs a multipoint locking system on a euro cylinder - and that calls for a different standard entirely.
For euro cylinder doors, the relevant standard is TS007. The aim is a 3-star TS007 rating - either a single 3-star cylinder, or a 1-star cylinder combined with 2-star door hardware that together reach 3 stars. The main failure mode on uPVC and composite doors is not lever picking; it is cylinder snapping. Forcing or snapping the euro cylinder bypasses the multipoint lock entirely, which is the attack that BS3621's lever testing was never designed to address.
This is worth knowing before you replace a lock or act on insurer advice about security. If your door is uPVC or composite, the conversation starts with the cylinder, not the mortice. We have pages on anti-snap cylinders and on uPVC door lock repair if that is the direction you need.
Getting British Standard locks fitted in Nottingham
If you are not sure what is on your door, or you know a lock needs replacing, Autelix operates across Nottingham as a mobile service - we come to the property. Checking your locks before a renewal rather than after a claim is the easier conversation to have.
If you need a lock change service in Nottingham, get in touch and we will assess what the door needs.
Frequently asked questions
Published: 14th August, 2026 | Updated: 14th August, 2026