There is a large range of security locks available to homebuyers.

Choosing a lock can be daunting, as two locks can look very similar but in fact be very different in terms of their security, quality and general reliability.

This document describes basic lock types and related British or European standards with which they may comply.

Lock Types

All locks consist of four main parts, the case, the key/locking mechanism, the lock bolt mechanism and its receiving recess.

The three basic forms of lock case are:-

Mortice Lock – A lock case designed to be fitted within the midrail of a door or window. Where a handle operated latch is incorporated, such locks are called ‘mortice sashlocks’.

Rim Lock – A lock case designed to be fitted on the internal surface of a door or window (these are now old fashioned and not considered to be particularly secure as they are only attached to the surface of the door by screws

Cylinder Locks – A lock where the key has a number of ridges along its length which, when the key is inserted into the cylinder, engage with sprung pins inside it. When all the pins are correctly raised the key can turn the cylinder to operate the lock.

Increasing the numbers of levers/pins allows for more key variations, thus making it harder for thieves to ‘pick’ the lock. 5 levers/pins is the usual minimum for a secure lock.

All locks have a lock bolt designed to move out of the lock case and engage in a suitable recess. Use of hardened steels, or inserts within the bolt, can hinder attack by cutting.

A ‘deadlocking’ lock bolt is one that, when in the locked position or the door is closed, cannot be pushed back into the lock case

A lock bolt recess will be in a frame or another door. To protect the edge of the recess from wear, it should have a metal ‘flush striking plate’ fitted; but ideally, to hinder attack on the bolt should have a ‘boxed striking plate’, i.e. one with an integral steel box to receive the bolt.

British Lock Standards

The security of a lock cannot reliably be assessed by simply looking at it, so tests that simulate common attack methods and usage are required. Of the various test standards that can apply to locks, the one most commonly cited by UK insurers is:-

BS 3621 – This test relates to mortice and cylinder rim locks for doors where a key is required for entry or exit. Such locks are most commonly identified by the BSI ‘kitemark’ marked on the lock face or packaging.

The latest version of BS 3621 matches a security level within BSEN 12209, but with locks also subjected to review for possible weaknesses by an expert UK panel.

Note. Some BS3621 rim locks have an internal handle that can override the key lock. If a letterbox/breakable glass is adjacent, the handle must be locked to maintain security.

Some other UK standards include:-

BS 8621 – A version of BS3621 that applies to locks requiring a key for entry but not for exit. Such locks are intended for use in upper floor flats with a single entry/exit door which is required to have an emergency thumb release on the inside to satisfy BS 5588 – Design, Construction & Use of Residential Buildings.