BS3621: The Lock Standard Your Insurer Assumes You Have
The quick answer
BS3621 is a wooden-door standard. It describes a mortice lock — the kind cut into the thickness of a timber door. If your front door is uPVC or composite, one physically cannot be fitted, no matter what your policy paperwork says. What those policies accept on a uPVC door is a TS007 3-star cylinder instead.
Plenty of houses need both: a British Standard mortice on the old wooden back door, and a 3-star cylinder on the composite front.
Check your own door in 60 seconds
Open the door and look at the edge, at the metal plate the bolt comes out of.
- See a stamped Kitemark and "BS3621"? You've got one. Nothing to do.
- See a lock but no Kitemark? It isn't British Standard. Five levers alone doesn't make it one — the mark is the certification, and plenty of five-lever locks have never been tested.
- No mortice lock at all, just a euro cylinder through the handle? Your door is uPVC or composite, and BS3621 was never the right question. Skip to the section below.
What BS3621 actually gives you
A key on both sides, and at least five levers on a mortice deadlock. The key-both-sides part is the security point: someone who breaks the glass in your door, or fishes through the letterbox, still can't turn the lock — provided you haven't left the key sitting in it. Which people do, constantly, because it's convenient.
That's also the trade-off, and it's worth saying plainly rather than glossing over it.
The bit most articles skip: getting out
A lock that needs a key on the inside is a lock you need a key to escape through. In a fire, at night, in smoke, that's a genuine problem — and it's why a second standard exists.
| Standard | Getting in | Getting out | Typically for |
|---|---|---|---|
| BS3621 | Key | Key | Houses with more than one exit |
| BS8621 | Key | Thumbturn, no key | Flats, HMOs, single-exit homes |
| BS10621 | Key | Locks from outside only | Uncommon, specific cases |
If your home has one way out, or you're in a flat, BS8621 is usually the right one — not the one people get sold. Keep a key by the door if you have BS3621, but somewhere it can't be reached through glass or the letterbox.
"No upselling, no nonsense, just honest work done properly. Finally feel confident my door is secure."
Tracey B, NottinghamIf your door is uPVC or composite
This is most people, and it's where the confusion does real harm. Your door doesn't have a mortice lock. It has a multipoint mechanism — hooks and bolts down the frame — driven by a euro cylinder, the barrel the key goes into.
So BS3621 isn't a thing you can buy for it. The standard that matters is TS007 3-star on the cylinder, and it addresses the actual weakness of these doors: snapping the cylinder in two, which takes seconds. Either a 3-star cylinder on its own, or a 1-star cylinder behind 2-star security handles.
There's a full guide to that here, including the thirty-second check for whether your cylinder is exposed enough to be gripped.
So what does your insurer want?
Read the wording. That's the only honest answer, because policies differ — some name a standard for final exit doors, others just require the property to be secured, and the phrasing often hasn't caught up with the fact that most front doors stopped being wooden decades ago.
What's fair to say: if your door can take a British Standard lock and doesn't have one, that's an argument waiting to happen after a break-in. Meeting the standard doesn't just satisfy a form — it removes the conversation entirely.
And if a locksmith quotes you for "BS3621 locks" on a uPVC door without blinking, that tells you something about the locksmith.
Getting it sorted
Not sure which camp your door is in? Send me a photo of the edge of the door and I'll tell you straight — no callout for that, and if it's already compliant I'll say so.
If it does need doing, it's a standard lock change at my published price, fixed before I start. Call or text 07414 727717 — I cover Beeston, Bulwell, Arnold, West Bridgford, Hucknall, Ilkeston and Derby.