Definitive guide · locks & insurance
BS3621 and home insurance: what your policy needs in 2026
BS3621 is the British Standard for a key-locking deadlock — five levers, a kitemark stamped on the faceplate. Most UK home insurance asks for it on the final exit door of timber doors; uPVC and composite doors are judged on the cylinder instead, usually a TS007 anti-snap one. A non-compliant lock can reduce or void a forced-entry claim, so it pays to check your own door before you ever need to.
Market rates vary widely. Our price: a fixed quote before any work starts — lock change / replacement from £99, total price — no VAT added.
- BS3621 = key-egress deadlock; BS8621 = thumbturn egress; TS007 = cylinder rating
- Insurers judge timber doors on the lock, uPVC and composite doors on the cylinder
- A missing kitemark can cut or void a break-in claim — not a fire or flood one
Most people first hear the term “BS3621” in a sentence they would rather not read: a declined insurance claim after a break-in. The standard is not bureaucracy for its own sake — it describes a lock that genuinely resists attack. The trouble is that the wrong standard, or a lock with no mark at all, can leave you uncovered at the exact moment you need the policy most. Here is what the letters mean, and how to check your own door.
What does BS3621 actually certify?
BS3621 is the British Standard for a thief-resistant deadlock that you lock and unlock with a key from both sides. To carry it, a lock must have at least five levers, a bolt that throws at least 20mm, and hardened protection against drilling, sawing and picking. It is the lock most timber-door policies name by default.
In plain terms, the standard exists because locks meeting it have been tested to hold up under the tools and time a real burglar uses. When your policy says “a lock conforming to BS3621”, it is borrowing that test result as a measure of your front door’s resistance.
How is BS3621 different from BS8621 and TS007?
They protect different things and are not interchangeable — using the wrong one is the most common mistake. BS3621 is key-operated both sides; BS8621 swaps the inside key for a thumbturn so you can escape without hunting for a key; TS007 rates the euro cylinder used on most uPVC and composite doors. This table is the heart of the subject:
| Standard | Covers | Egress (inside) | Where it usually applies |
|---|---|---|---|
| BS3621 | Mortice deadlock / sashlock | Key both sides | Final exit, timber doors |
| BS8621 | Mortice deadlock | Thumbturn (keyless out) | Flats, fire-escape routes |
| BS10621 | Mortice deadlock | Key out, lockable thumbturn | Mixed-use, dual mode |
| TS007 | Euro cylinder (star rating) | n/a — cylinder only | uPVC & composite doors |
The catch many owners miss: a uPVC door almost never has a BS3621 mortice lock at all. Its security lives in the cylinder, so the relevant standard is TS007 — ideally a 3-star anti-snap cylinder, or a 1-star cylinder paired with 2-star door furniture. Naming BS3621 on a uPVC door is a sign a policy was written for a timber door it does not have.
How do I check my own door in two minutes?
Open the door wide and read the faceplate on the door edge: a compliant lock has the BSI kitemark and the standard number stamped into the metal itself. No stamp means no certification, no matter what the previous owner or the box claimed. That two-minute look is worth more than any assumption.
Work through it door by door:
- Open the door fully so you can see the faceplate on the closing edge, not just the handle.
- Find the kitemark. Look for the BSI heart-shaped mark and “BS 3621” etched into the metal — printed stickers do not count.
- Count the cuts on the key. A five-lever lock has five distinct cuts on the blade; three cuts is a three-lever lock and not BS3621.
- On a uPVC or composite door, read the cylinder instead. Look for a TS007 star rating or a Kitemark on the cylinder or handle, since BS3621 does not apply there.
Will a missing kitemark really void my insurance?
Not automatically, and not for every claim — but for a forced entry through the non-compliant door, an insurer can reduce or refuse the payout if that lock was a stated condition. A claim unrelated to entry, such as a burst pipe, is not affected. The honest summary: compliance is cheap insurance for your insurance.
The worst moment to discover a shortfall is while filing a claim, because that is exactly when an assessor checks the faceplate. Bringing a door up to standard costs far less than the gap between a full payout and a reduced one. If your policy names a standard your door does not meet, treat it as a job to book, not a risk to sit on.
What insurance-ready locks typically cost
These are broad UK market figures, not our prices — they move with the door, the brand and who fits them. We keep our own number separate and fixed, below the table, so you are never comparing a range against a guess.
| Job | Typical cost | Time it takes |
|---|---|---|
| BS3621 mortice deadlock, fitted | £90–160 | 30–60 minutes |
| BS3621 sashlock, fitted | £110–180 | 30–60 minutes |
| TS007 3-star anti-snap cylinder, fitted | £80–140 | 15–30 minutes |
| Full front-door upgrade | £160–260 | Half a day |
When is this a job for a locksmith, not a DIY swap?
Stop and call once the door is timber and needs a mortice cut, the cylinder sizing is uncertain, or your policy names a standard you cannot confidently match by eye. Guessing the cylinder length is the classic DIY trap — too long and it is a snapping risk, too short and it will not lock.
A locksmith reads the policy wording against the actual door, fits a lock that carries the mark the insurer named, and gives you the paperwork — receipt, specification, photos of the kitemark — that makes a future claim a formality rather than an argument. For where each standard sits in the wider hierarchy, our note on understanding lock grades goes a level deeper.
Questions people ask us
How do I tell if a lock is genuinely certified?
Open the door and read the lock's faceplate, the metal strip on the door edge. A certified lock carries the BSI kitemark and the standard number stamped into the metal, not printed on a sticker or the box. No mark on the faceplate means no certification, whatever the seller claimed.
Can my insurer really refuse to pay over a lock?
For a forced-entry claim, yes — if your policy made a specific lock a condition and the door did not meet it. Courts expect proportion, so a minor shortfall is more likely to cut a payout than cancel it. Unrelated claims, like fire or flood, are not affected. Read your policy wording.
I live in a listed building and can't fit modern locks — what now?
Tell your insurer in writing before anything happens, not after. Where conservation rules block a certified lock, many insurers will accept an equivalent or endorse the policy with alternative wording. Document the constraint and whatever security you do have, and keep that note with your policy.
Do I need to tell my insurer after I upgrade my locks?
It is not usually required when you are simply meeting a condition you already agreed to, but it does no harm and occasionally trims a premium. Either way, keep the fitting receipt and a photo of the kitemark with your policy documents — that paperwork is what settles a dispute quickly.
Are window locks part of the same requirement?
Often, yes. Many policies ask for key-operated locks on accessible and ground-floor opening windows, though the wording is usually looser than for doors. Check the security conditions section of your policy for the exact phrase that applies to your home.
If it comes to it
Want a number instead of a theory?
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Sources
- BSI — BS 3621:2017 Thief-resistant lock assembly — knowledge.bsigroup.com
- Association of British Insurers — Securing your home — abi.org.uk
- Secured by Design — Doors and locks guidance — securedbydesign.com
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