Mortice Locks

Aged Brass 3" 5 Lever BS Dead Lock, from our current range.

What is a mortice lock?

A mortice lock is a lock body fitted into a pocket, or mortice, cut into the leading edge of the door itself, rather than mounted on the door's surface. This gives a stronger, more concealed fixing than a surface-mounted lock, which is why mortice locks remain the standard specification on most timber front and back doors in the UK, and are frequently required by home insurance policies.

"Mortice lock" is really an umbrella term covering several specific types, most importantly the sashlock, which combines a lock with a handle-operated latch, and the deadlock, which locks and unlocks by key only.

Where mortice locks are used

• Timber front and back doors – the standard lock type on solid timber doors, often required for insurance purposes
• Internal doors – smaller mortice locks are used on internal doors needing a lockable option, such as a home office
• Period properties – mortice locks are the traditional choice and remain widely specified on period doors today

Choosing the right mortice lock

A few practical points are worth checking before you buy:

• British Standard certification – look for BS3621 or equivalent if your insurance policy requires it
• Case size – mortice locks are sold in different case sizes (commonly 2½" and 3"); check this matches your door and existing mortice if replacing an old lock
• Sashlock or deadlock – decide whether you need a combined latch and lock, or a lock-only mechanism
• Keyed alike – if fitting several doors, a keyed alike set lets one key operate them all

Related products

Browse our current range in Locks & Latches, or see the related Sashlocks and Deadlocks guides.

Frequently asked questions

What size mortice lock do I need?

Mortice locks are commonly available in 2½" and 3" case sizes; the right size depends on your door's stile width. If replacing an existing lock, matching the current case size avoids enlarging the mortice.

Do I need a British Standard mortice lock?

Many UK home insurance policies require BS3621 or equivalent locks on external doors. It is worth checking your policy before buying.

Can a mortice lock be fitted to any timber door?

Most solid timber doors can accept a mortice lock, provided the stile is wide enough for the case size chosen. Thinner or glazed doors may need a different lock type.

Back to the Locks & Security Guide, or explore the full Knowledge Centre.