Which front door lock do I actually need?

Door security is written into most home insurance policies, and the wording is specific. Fitting the wrong thing is not just less secure — it can be the difference between a claim being paid and not.

What you'll need

• Your insurance policy wording
• A look at the existing lock's forend markings
• A tape measure if replacing a cylinder

Step by step

1. Read your policy first.Most UK policies specify a minimum standard for final exit doors. The exact wording matters, and it is usually one short paragraph.
2. Identify what door you have.Timber doors take mortice locks and rim cylinder nightlatches. uPVC and composite doors take a multipoint strip operated by a euro cylinder. The standards differ accordingly.
3. On timber, look for BS3621.A five-lever mortice deadlock carrying the BSI kitemark and BS3621 on the forend. This is the standard insurers name most often, and a 'five lever' lock without the kitemark does not meet it.
4. Understand the BS3621 family.BS3621 is key-locking from both sides. BS8621 is keyless egress from inside, used where escape matters. BS10621 locks the inside handle only when locked externally, for holiday homes.
5. On uPVC, look at the cylinder standard.TS007 3-star, or TS007 1-star cylinder plus a 2-star security handle, or Sold Secure Diamond. These test specifically against snapping, which is the main attack on euro cylinders.
6. Check the cylinder projection.A cylinder standing proud of the handle by more than 3mm gives an attacker something to grip. It should be as close to flush as possible.
7. Consider the whole door, not just the lock.Hinge bolts on a timber door, a solid frame properly fixed, laminated glass in any panel within reach of the lock, and a letterplate cowl all matter as much as the lock grade.
8. Check the nightlatch too.A rim nightlatch is not a deadlock. Many policies require a nightlatch to be BS3621 as well, or accept a basic one only alongside a compliant mortice deadlock.
9. Fit or specify like for like.Replacing a euro cylinder is straightforward. Fitting a mortice deadlock into a door that has never had one means cutting a large mortice, which is a job worth handing over.

Tips

• The cheapest meaningful security upgrade on a uPVC door is a 3-star anti-snap cylinder. It costs less than a takeaway and directly addresses the most common break-in method.
• Measure a euro cylinder from the central fixing screw to each face separately — they are frequently asymmetric, such as 35/45.
• If glass sits within arm's reach of a thumbturn, a thumbturn is a liability rather than a convenience.

Common mistakes

• Assuming any five-lever lock meets the standard — BS3621 tests resistance to drilling, picking and forcing, not just the lever count. A five-lever lock without the kitemark can fail a policy condition even though it looks identical from the inside.
• Fitting a cylinder that sticks out past the handle — A proud cylinder can be gripped and snapped in seconds. Even a high-rated cylinder is weakened by being fitted too long, so measure the door and buy the correct length.

Alternatives

• Five-lever mortice deadlock, BS3621: The insurance default on timber doors. Locked with a key from both sides, no handle involvement, bolt throwing deep into the frame.
• Anti-snap euro cylinder, TS007 3-star: The correct answer on uPVC and composite doors. Sacrificial sections break away leaving the lock intact if the cylinder is attacked.
• Rim nightlatch to BS3621: A deadlocking nightlatch for convenience plus security. Useful as a second lock, not usually accepted alone.
• Smart lock: Convenient, but check it carries the same standards. Many are not tested to BS3621 or TS007 and are not accepted by insurers on their own.

Questions people ask