What Is a BS3621 Deadlock?
BS3621 is a British Standard for thief-resistant locks. A mortice deadlock that meets BS3621 has been independently tested and certified to resist common attack methods including picking, drilling, and forcing. It's the standard that virtually all UK home insurance policies require for timber door security.
How BS3621 Deadlocks Work
A BS3621 mortice deadlock is a 5-lever mechanism housed inside a pocket (mortice) cut into the edge of a timber door. When locked, a hardened steel bolt extends into the door frame, securing the door against forced entry. Key features:
- 5-lever mechanism — offers over 1,000 key combinations, making picking extremely difficult
- 20mm hardened steel bolt — minimum throw distance, resistant to sawing and forcing
- Anti-drill protection — hardened plates or pins protect the mechanism from drill attacks
- Key operated from both sides — provides security even if glass near the door is broken
- Boxed keep/strike plate — reinforces the frame side of the lock
Brands We Recommend
ERA Fortress — Best Value
Reliable BS3621 certified deadlock with anti-pick and anti-drill features at an affordable price point. Widely available and fits standard mortice cutouts.
Union 2134 — Professional Choice
A favourite among locksmiths for its smooth operation and robust build quality. 6-pin anti-pick mechanism exceeds BS3621 requirements.
Chubb 3G114 — Premium Security
Chubb (now part of Yale) 3G114 is a high-security option with additional anti-manipulation features. Excellent for high-risk properties.
Do I Need a BS3621 Lock?
If your front door is timber (wood), almost certainly yes. Most UK home insurance policies require BS3621 locks on all final exit doors. A "final exit door" is any external door that could be used to leave the property — front, back, and side doors.
Important: If you don't have BS3621 compliant locks and make a burglary claim, your insurer may refuse to pay out. Check your policy documents or call your insurer to confirm.
BS3621 vs Non-Standard Mortice Locks
Older properties often have 2-lever or 3-lever mortice locks that look similar to BS3621 locks but offer significantly less protection. You can usually identify the standard by looking for the BS kitemark on the faceplate (the metal plate visible on the door edge). No kitemark = not BS3621.
Professional Fitting
Installing a mortice deadlock requires cutting a precise pocket into the door edge. This should be done by a professional locksmith to avoid weakening the door. Our lock replacement service includes expert fitting with all timber door work.
Call 0330 133 1339 — available 24/7 across all our service areas.