Most British front doors use one of four locking systems: a multipoint lock, a mortice deadlock, a nightlatch, or a combination of the last two. Which one you have decides what you can upgrade and what your insurer expects. The cylinder is usually the part worth changing, and it is the cheapest security improvement available on any door.
Multipoint lock. Standard on modern doorsets in every material. Lifting the handle throws bolts, hooks or rollers into the frame at several points up the height of the door, then the key locks them there. It spreads the load and it is why a modern door resists being levered.
Mortice deadlock. A lock set into the edge of a timber door, throwing a single square bolt into the frame. Operated by key from both sides, and common on older timber doors, often paired with a nightlatch above it.
Nightlatch. The sprung latch that closes when you pull the door shut, key from outside and knob from inside. On its own it is a convenience rather than a security measure, which is why it sits above a deadlock rather than instead of one.
Slam lock. A multipoint lock that engages when the door closes rather than when the handle is lifted. Common on communal entrances and on doors people go in and out of all day.
Open the door and look at the edge of the leaf.
A long metal strip running most of the height of the door, with several bolts or hooks along it, is a multipoint lock. A single square bolt in a small faceplate is a mortice deadlock. A sprung wedge-shaped latch is a nightlatch.
Then look at the keyhole. A shape like a fat keyhole with a round top and a wider bottom is a euro cylinder, which is what almost all multipoint locks use. A plain rectangular slot is a mortice key.
For a modern door, a multipoint lock with a three star cylinder. For an older timber door, a BS3621 mortice deadlock with a nightlatch above it. Those two answers cover most British front doors.
The reason the cylinder gets named rather than the lock is that the cylinder is where the attack happens. A multipoint lock is difficult to force and easy to bypass through a weak cylinder, so upgrading the cylinder upgrades the door.
Beyond that, the lock matters less than the fit. A door hanging out of square puts the bolts under load they were not designed for, and the strongest lock in the world is bolted to a frame.
TS007 is the British kitemark scheme for door cylinders and handles, and it is scored in stars. The system is designed so that stars add up.
The practical version: get to three stars, either with a three star cylinder on its own or with a one star cylinder behind a two star handle. Which route you take depends on what your door already has.
Home insurance policies frequently specify a lock standard, and the one that appears most often is BS3621 on the final exit door. A policy can also require key-operated locks on accessible windows.
Read your policy wording rather than assuming. It matters at the point of a claim, and it is the one part of this page that can cost you money after the event rather than before it.
If your door has a multipoint lock rather than a mortice, check how your insurer treats it. Policy wording written around mortice locks does not always translate cleanly.
A euro cylinder comes out on a single screw through the edge of the door, below the latch, and the whole job takes ten minutes.
Measure the old one before you buy. A cylinder is quoted as two figures, for example 40/50, measured either side of the central screw hole. Too short and the key will not reach. Too long and it stands proud of the handle, which is a weakness in itself.
