What is BS3621 and how do I know if my lock is BS3621?

BS3621 is a British Standard for thief-resistant mortice locks and cylinders, tested for resistance to picking, drilling and manipulation. A genuine BS3621 lock carries a small embossed kitemark on the faceplate or forend — the metal edge visible when the door is open. It usually sits alongside the letters BS3621 and a date. If you cannot see a kitemark, the lock is very likely not certified, whatever the seller may have called it.

What does BS3621 mean on a lock?

It means an independent test has checked the lock against a published British Standard covering strength, key security and resistance to common attack methods. It is not just the seller calling it 'high security'. It is the specification most UK home insurers reference when they ask for a five-lever mortice lock or an equivalent standard on final exit doors.

Is my lock insurance approved?

That depends entirely on your policy wording, which is worth checking directly rather than assuming. Many UK insurers specifically name BS3621, so a lock without the kitemark can leave a claim open to dispute even if the lock itself feels secure. Checking the actual policy document is the only reliable way to know.

What's the difference between BS3621 and TS007?

BS3621 covers traditional mortice locks and cylinders fitted into the door edge. TS007 is a separate standard, rated in stars, that covers euro cylinders — the round barrel locks used in uPVC and composite multipoint doors. A door with a euro cylinder needs a TS007-rated (or equivalent anti-snap) cylinder rather than a BS3621 mortice lock. That is because the two standards apply to different lock types.

Guide

BS3621 Explained: What It Means for Your Front Door Lock

Name: Bayswater Locksmiths
Price range: ££

What BS3621 means, how to check if your lock meets it, why UK insurers ask for it on final exit doors, and how to upgrade a front or back door lock in London.

Written by Bayswater Locksmiths · last reviewed 8 September 2026

BS3621 is the British Standard for thief-resistant mortice locks. It is what most UK home insurers mean when a policy asks for a “five-lever mortice lock” or “British Standard lock” on final exit doors. A genuine BS3621 lock has been tested against picking, drilling and forced attack. It carries a small embossed kitemark on the faceplate to prove it.

A lock without that mark is not certified, whatever the seller called it. Checking for the kitemark takes thirty seconds and is the single most useful thing to do before assuming a policy requirement is already met.

What BS3621 actually tests

The standard covers the mortice lock body and cylinder together, not just the visible cylinder cap. Testing includes resistance to lock-picking, drilling, and physical attacks such as levering or snapping. It also sets a minimum number of key differs (unique key combinations), so that keys are not easily duplicated or guessed. A lock that passes carries the kitemark and the standard number, applied by the manufacturer under an accreditation scheme rather than self-certified.

How to check whether your lock is BS3621

Open the door and look at the forend: the metal edge plate visible on the door face when it is open. This is where the lock body sits in the wood or uPVC. A genuine BS3621 lock shows a small embossed kitemark, usually with “BS3621” and a year stamped nearby.

If there is nothing there, or the marking is unclear, that is worth treating as “not confirmed” rather than assuming the best. A locksmith can check this for you on a visit and advise whether the existing lock body is worth keeping or replacing.

Why insurers ask for it

Most UK home insurance policies specify a minimum lock standard on final exit doors as a condition of cover. BS3621 is the specification named most often. This is not a formality: if a claim follows a break-in and the lock did not meet the policy’s stated requirement, an insurer can dispute or reduce the payout, even where the burglary itself was not in question.

Checking the actual policy wording is the only way to know for certain what your specific insurer requires, rather than assuming what “standard” locks usually mean.

BS3621 vs TS007 vs anti-snap

BS3621 applies to traditional mortice locks fitted into a timber or composite door edge. Most modern uPVC and composite doors use a different mechanism entirely: a multipoint lock operated by a euro cylinder, the round barrel visible through the door handle. That cylinder is covered by a separate standard, TS007, rated from one to three stars for resistance to lock snapping. Snapping is a well-known weakness in older, unrated euro cylinders.

In practice, a timber front door with a mortice lock needs BS3621. A uPVC or composite door with a multipoint mechanism needs a TS007-rated or anti-snap euro cylinder instead. See the anti-snap euro cylinders page for that side of it.

Upgrading to BS3621

Where a mortice lock does not carry the kitemark, upgrading usually means replacing the lock case itself rather than just a cylinder. That is because the standard applies to the whole mechanism.

This is a common job to combine with a routine lock change. While the old lock is out, fitting a certified BS3621 case costs little extra in time and closes the insurance gap in one visit. For dedicated BS3621 fitting and product options, see the BS3621 locks service page.

Flats, communal doors and mansion blocks

In blocks with a shared entrance, the front door of your own flat is usually your responsibility. The communal door is typically the freeholder’s or managing agent’s. Both matter for insurance.

Your own final exit doors need to meet your policy’s lock standard. A poorly secured communal entrance, meanwhile, is worth raising with the managing agent as a shared security issue rather than something a leaseholder can fix alone. If your building has period ironmongery or a listed-status entrance, see the period property security guide for how to upgrade sympathetically rather than replacing original features outright.

Getting a BS3621 lock fitted

Send us the door type and roughly how many locks need checking, and you will get a clear price before anyone travels. Get in touch: request a call back or use the contact page to arrange a BS3621 check or upgrade.