BS3621, TS007, SS312: Which Lock Standard Your Door Actually Needs
Lock standards are where good intentions go to get confused. A homeowner reads that they need a British Standard lock, checks their insurance small print, sees a reference to BS3621, and reasonably assumes that one code covers every door in the house. It does not. The standard that protects a wooden front door is not the standard that protects a uPVC or composite one, and applying the wrong one, or assuming a single certificate covers the lot, is one of the most common mistakes in domestic security. Getting it right is not complicated once someone lays it out door by door.
Because the numbers get quoted loosely across the internet, it is worth having them explained by someone who works to them daily. LocksmithLocal's locksmiths are trained to the accredited standard and fit to these codes as a matter of routine, so here is the plain-English version of what each one means and, more importantly, which door each one belongs to. Once the mapping is clear, the small print on your insurance policy stops being intimidating.
Start with BS3621, because it is the one most people have heard of and the one most often misapplied. BS3621 is the British Standard for a key-operated lock, typically a five-lever mortice deadlock, of the kind fitted to a timber door. It is a timber-door standard. If you have a traditional wooden front or back door, this is the code your insurer most likely expects to see, and a good BS3621 mortice lock is a serious piece of security. The trouble starts when this timber-door standard gets quoted at owners of uPVC and composite doors, which do not use a mortice lock at all and cannot meet BS3621 in the way a wooden door does. They are secured on an entirely different principle.
That different principle is the multipoint lock and the euro cylinder, which is where TS007 and SS312 come in. A modern uPVC or composite door locks at several points around the frame when you lift the handle, and the part a would-be intruder actually attacks is the euro cylinder, the barrel that the key goes into and that protrudes slightly from the handle. The single most common forced-entry method on these doors is snapping that cylinder, and the anti-snap standards exist precisely to defeat it. This is a genuinely different security problem from a wooden door, and it needs its own answer.
TS007 is a three-star rating system, and this is where the detail matters because most guides skip it. You can reach the full three-star protection in one of two ways. Either you fit a single three-star cylinder that has passed the test on its own, or you combine a one-star cylinder with a two-star security handle, and one plus two makes the three-star combination. Both routes get you to the same place. What you must not do is fit a one-star cylinder on its own and assume you are protected, because a one-star cylinder without the matching handle is only part of the system. Knowing this stops you buying half a solution and believing it is whole.
Sold Secure SS312 Diamond is the other name you will see, and it sits alongside TS007 as an anti-snap benchmark. SS312 Diamond is generally regarded as the tougher of the two tests, because it is assessed against a heavier set of tools and attack methods. A cylinder carrying the SS312 Diamond mark is a strong choice for a euro-cylinder door, and many of the best cylinders on the market carry both TS007 three-star and SS312 Diamond approval. If you are choosing a new cylinder for a uPVC or composite door and you see the Diamond mark, you are looking at hardware that has been through a demanding independent test.
The practical upshot is a simple map. If your door is timber and key-operated, BS3621 is your standard and a quality five-lever mortice lock is what you want. If your door is uPVC or composite with a multipoint mechanism and a euro cylinder, your protection rides on that cylinder meeting TS007 three-star or SS312 Diamond, whether through a three-star cylinder alone or the one-star-plus-two-star-handle route. One house can easily need both standards, a BS3621 lock on the old wooden back door and a three-star cylinder on the composite front door, and there is nothing odd about that.
This also clears up a question that causes real anxiety, which is insurance. Insurers care about the standard your locks meet, and a claim can be complicated if the hardware does not match what the policy requires. The reassuring news is that meeting these standards is entirely achievable and usually not expensive relative to the protection it buys. The confusion almost always comes from a mismatch, a timber-door standard quoted at a composite door, or a one-star cylinder mistaken for full protection, rather than from the standards themselves being unreasonable.
The reason this matters beyond passing an insurance check is that the right standard genuinely resists the attack your door is likely to face, and the wrong one leaves a real gap. A snappable cylinder on a composite door is a known weakness with a known fix. If you are unsure what you currently have, an accredited locksmith can identify your cylinder and lock type in a couple of minutes, tell you which standard applies to each door, and fit the correct hardware where there is a shortfall. There is no need to guess your way through the small print alone.
