You've got a letter from your home insurance asking whether your locks are British Standard. Or a renewal quote has gone up and the small print mentions BS3621. Or you've just bought a house and the solicitor's pack flagged the locks as non-compliant. This is the post that explains, in plain English, what BS3621 is, why it matters, and what to do about it.

The short version

BS3621 is the British Standard for thief-resistant locks fitted to final exit doors of a home — i.e. front and back doors, plus any external side door. It's a specification covering drill resistance, pick resistance, key cycles, key combinations, anti-saw and anti-bolt-thrust requirements. Locks certified to BS3621 carry a Kitemark stamp from the British Standards Institution and the BS3621 reference on the lock faceplate.

Most UK home insurance policies require BS3621 on every final exit door. Without it, a claim after a forced entry can be reduced or refused. The standard has existed in some form since 1980, with the current version (BS3621:2007 plus amendments) being what insurers reference today.

What BS3621 actually covers

The standard sets minimum requirements on a long list of attack vectors. The headline ones:

Drill resistance: hardened steel components at the points an attacker would target with a power drill.
Pick resistance: a minimum number of differs (key combinations) and design features that defeat raking and bumping attacks.
Saw resistance: hardened anti-saw rollers in the bolt.
Bolt thrust: minimum bolt projection (usually 20mm) and resistance to being forced back into the case.
Key cycles: the lock must withstand at least 100,000 unlock cycles without failure.
Strike plate strength: the strike (the part fitted to the door frame) must resist a defined load.

The result is a lock that takes minutes to defeat with hand tools and resists most common burglary methods. Not invincible — nothing is — but a meaningful step up from a non-certified 5-lever, and a huge step up from a non-deadlocking nightlatch.

Why insurance asks for it

UK home insurance evolved alongside the British Standards. By the late 1990s most insurers had standardised on BS3621 as the minimum lock spec for final exit doors for the policy's burglary cover to apply at the policy's stated terms.

In practice this means:

Your policy schedule or terms include a wording like "all final exit doors must be fitted with locks conforming to British Standard BS3621".
If you make a burglary claim and the loss adjuster finds the locks don't meet that spec, they can apply a settlement reduction or, in serious cases, refuse the claim.
"Final exit door" is interpreted broadly — front, back, side doors. A door that opens to the outside, with no other door between it and the outside world, counts.

The risk is highest on wooden front doors in older terraces and conversions where the original mortice was fitted before the current BS3621 came into force. We see this routinely on older stock around Chorlton, Didsbury, and parts of the City Centre.

How to tell if your locks meet BS3621

The faceplate test:

Open the door and look at the edge of the door — the strip of metal where the bolt comes out (the faceplate).
Look for the Kitemark — the BSI Kitemark is a stylised heart-shape logo. Underneath it should read "BS3621" with a year (usually 2007, sometimes 2004).
No mark, no certification. If the faceplate is blank or has only a brand logo with no Kitemark or BS3621 number, the lock is not certified — even if it looks superficially like one that is.

A few caveats:

Brand alone doesn't tell you. Some brands (Chubb, Yale, Union) make both BS3621-certified and non-certified locks. The mark on the faceplate is what counts.
Older five-lever mortice locks from before the standard existed look very similar to current BS3621 locks but are not certified.
The Kitemark on the box isn't enough — what's stamped on the lock itself is what counts. Some lookalike products list the standard on the packaging but aren't certified.

If you can't tell, we'll check for you in five minutes during any other visit — or as a standalone fast check.

What BS3621 doesn't cover

Important: BS3621 applies to mortice locks (the type fitted into a pocket in the door edge, typical on wooden doors). It does not apply to:

Euro cylinder locks on uPVC and composite doors — these need a TS007 3-star or Sold Secure Diamond rating (the anti-snap standard). We cover this in are anti-snap locks worth the extra cost?.
Multipoint mechanisms in uPVC doors — the strip with hooks and bolts that runs the length of the door.
Nightlatches and rim cylinders — the spring-loaded latches sometimes fitted as a secondary lock on wooden doors. Some are BS3621-certified, but on their own they don't meet most insurance requirements without a deadlocking mortice as well.

So if your insurance says "British Standard locks on all final exit doors" and you have a uPVC door, what they actually mean is an anti-snap cylinder. If you have a wooden door, what they mean is BS3621.

What a BS3621 lock costs to fit in Manchester

Fitted prices in 2026:

BS3621 5-lever mortice deadlock fitted (standard wooden door, existing mortice pocket suitable): £140–£280 including the lock.
Same job with mortice pocket enlargement (older door, smaller pocket): add £30–£50 in labour.
BS3621 mortice plus replacement nightlatch to bring the whole door up to spec: £200–£380.

Fitting time on a standard wooden front door is 60–90 minutes. We'd also check the strike plate fitting, the door alignment, and the frame around the lock — the lock is only as good as what it's bolted into.

Full pricing on our lock replacement page.

When to upgrade

If any of these apply, get it done:

Your insurance renewal letter mentioned BS3621
The lock faceplate is unmarked
The lock pre-dates the house (some sellers leave a 1970s lock in a 2010 door)
You've just moved in and don't know what's fitted
You've had a burglary or attempted break-in — see burglary repairs

The cost of compliance is far smaller than the cost of a refused claim, and the lock itself is better hardware regardless of the paperwork.

When to call us

Call us if you're unsure whether your locks meet BS3621, if your insurance has flagged it, or if you want it sorted properly before the renewal date. We work across Manchester every day. If you can send us a photo of the lock faceplate, we can usually tell you on the phone whether you're compliant or not, no visit needed.

BS3621 explained — what your insurance is actually asking for