Lock Types Explained — and the British Standards Behind Them

A quick word on the British Standards (it’s about the door, not “better vs worse”)

You’ll see several BS numbers. They’re not a quality ranking — they suit different door situations, mostly driven by how you need to escape in a fire:

• BS3621 — needs a key to lock AND unlock from both sides. The usual choice for domestic timber front/back doors. Once the key’s removed, a burglar can’t open it by reaching through the letterbox or breaking nearby glass.
• BS8621 — key to get in, but a thumbturn to get out (no key needed to exit). Common on flats and shared buildings where you must be able to escape quickly. Caution: don’t fit where a letterbox or glass panel lets someone reach the thumbturn.
• BS10621 — like BS8621 but the keyless exit can be switched off with a key from outside. Uncommon; used in some commercial “last one out locks up” setups.
• 3G114 — the British Standard marking you may see on older mortice locks; part of the same thief-resistant mortice-lock family as BS3621.

All are independently tested to comparable security criteria. The right one depends on your door and your escape route — we’ll advise.

Mortice deadlocks (timber doors)

A deadlock sits inside the body of the door and throws a solid bolt into the frame. Found mostly on wooden front and back doors.

• Standard (non-BS): a 2- or 3-lever mortice lock. Cheaper, but easier to pick/force and usually not accepted by insurers as sufficient on an exit door.
• British Standard (BS3621 / 3G114): at least five levers, anti-pick features, a hardplate to resist drilling, and a bolt that throws a solid distance into the frame. This is what most insurers expect on timber exit doors — check your policy wording.

How to tell: open the door and look at the faceplate on the edge for the BSI Kitemark and “BS3621” (or “3G114” on older locks). Important — not every 5-lever lock is British Standard; it must carry the stamp.

Rim cylinder nightlatches (the “Yale-style” latch)

The surface-mounted latch on the inside face of many timber doors that locks automatically when the door shuts.

• Standard nightlatch: convenient, but on its own it’s basic security — and usually not enough for insurance by itself.
• British Standard nightlatch (BS3621): a heavier-duty version that can be deadlocked with a key, with anti-drill and stronger components. These do meet the standard.

Key point: a basic nightlatch alone is rarely accepted by insurers. It’s normally fine only when paired with a BS3621 mortice deadlock on the same door. If a nightlatch is your only lock, that’s worth addressing.

Euro & rim cylinders — and the 1/3-star anti-snap ratings

The cylinder is the barrel the key goes into. On uPVC/composite doors it’s a euro cylinder; rim cylinders feed nightlatches. Cylinders have their own security ratings, separate from the BS3621 lock-body standards:

• Standard cylinder: vulnerable to “snapping” — a fast, low-skill attack that defeats most standard cylinders in seconds.
• 1-star (TS007): resists picking, drilling, bumping and plug extraction. Not fully snap-tested on its own.
• 3-star (TS007) / SS312 Diamond: all of the above plus anti-snap protection on its own. This is the level to look for on uPVC/composite doors, and what many insurers now expect there.

So which lock do I need?

• Timber front/back door (house): usually a BS3621 five-lever mortice deadlock, often plus a BS3621 nightlatch.
• uPVC / composite door: multi-point lock plus a TS007 3-star or SS312 cylinder.
• Flat / shared building main door: often BS8621 (keyless exit) for fire safety — check your building rules and your policy.
• Commercial / shared exit: BS8621 or occasionally BS10621.

Always check your own insurance wording, and if in doubt, ask us or your insurer directly.

Lock type FAQs

Is “3G114” a better lock than BS3621?

No — 3G114 is an older British Standard marking for thief-resistant mortice locks, part of the same family as BS3621. If you see it stamped on an older mortice lock, it’s a British Standard lock.

Is my Yale nightlatch enough for insurance?

A basic nightlatch alone usually isn’t. A BS3621 nightlatch, or a basic one paired with a BS3621 mortice deadlock on the same door, is what’s typically needed — check your policy wording to confirm what your insurer requires.

My door has a thumbturn inside — is that a problem?

That’s a BS8621-type lock, designed for keyless escape (good for flats/fire safety). It’s only a risk if a letterbox or glass panel lets someone reach the thumbturn from outside — we can advise on guards or alternatives.

Wooden door vs uPVC — different locks?

Yes. Timber doors use mortice deadlocks (BS3621 family); uPVC and composite doors use multi-point locks with rated cylinders (TS007 3-star / SS312). Different standards apply to each type of door.

Related guides

Deadlocks & Home Security · Lock Changes Finsbury Park · Emergency Locksmith

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