Mortice deadlock works with a key-driven bolt that slides into a strike plate
A mortice deadlock is fitted inside a rectangular pocket, called a mortice, cut into the edge of the door. Turning the key rotates a mechanism that extends a single bolt horizontally into a strike plate fixed to the door frame. The bolt is a deadbolt, meaning it cannot be pushed back without the key. This provides basic resistance to forced entry. This type of lock is common on older UK doors, particularly those built before the 1990s, and is often made by brands such as Union or Yale. For security, a mortice deadlock should meet British Standard BS 3621, which sets requirements for thief-resistant locks, including a minimum 20mm bolt throw and hardened steel inserts. Look for the BSI Kitemark on the lock body to confirm it meets the standard (GOV.UK, British Standards for locks, 2026).
A front door lock works by turning a key to extend bolts into the door frame. Mortice deadlocks use a single deadbolt, while multi-point systems lock at three to five points. Both types rely on the key to retract the bolts for entry.
- Mortice deadlocks use a single deadbolt that slides into a strike plate.
- Multi-point systems lock the door at three to five points with one key turn.
- Mortice deadlocks should meet British Standard BS 3621 for security.
- Multi-point locks are standard on uPVC, composite, and aluminium doors since 2000s.
- Replace only the Euro cylinder if a multi-point lock is damaged or keys lost.
- Mortice deadlock works with a key-driven bolt that slides into a strike plate
- Multi-point locking system secures the door at three to five points with a single turn of the key
- Quick numbers, cost, security, and installation for both lock types
- The front door lock works by engaging the bolt into the door frame when the key is turned
- BS 3621 is the minimum security standard for a front-door mortice deadlock in the UK
- How to verify a lock installer, MCS, FENSA, or TrustMark certification matters
Multi-point locking system secures the door at three to five points with a single turn of the key
A multi-point locking system uses a central gearbox, often powered by a Euro-profile cylinder, to drive hooks, rollers, or bolts that engage with keepers at multiple positions along the door edge. These positions are typically at the top, bottom, and middle of the door. The cylinder is the part you turn with the key, and replacing just the cylinder is common if the lock is damaged or keys are lost. This system is standard on most modern uPVC, composite, and aluminium front doors sold in the UK since the 2000s. For security, many models meet PAS 24, an enhanced security test for doorsets, or are certified to Secured by Design standards (Secured by Design, PAS 24:2022, 2026).
Quick numbers, cost, security, and installation for both lock types
| Feature | Mortice deadlock | Multi-point locking system |
|---|---|---|
| Typical lock cost (parts only) | £15–£50 | £40–£150 |
| Typical installation cost (labour) | £50–£100 | £80–£200 |
| Security standard (common minimum) | BS 3621 | PAS 24 or Secured by Design |
| Number of locking points | 1 | 3 to 5 |
| Common door material | Timber | uPVC, composite, aluminium |
Cost figures are based on 2026 average price data from Checkatrade and MyBuilder for lock replacement services (Checkatrade, 2026). Security standards are defined by the British Standards Institution for BS 3621 and Secured by Design for PAS 24.
The front door lock works by engaging the bolt into the door frame when the key is turned
In a mortice deadlock, turning the key rotates a cam that pushes the bolt sideways into a strike plate fixed to the frame. This is simple use. In a multi-point system, turning the key rotates the cylinder, which moves a central gearbox that simultaneously pushes hooks, rollers, or bolts into keepers on the frame at multiple points. Both mechanisms rely on the key aligning internal pins or discs inside the cylinder or lock body to allow rotation. If the wrong key is used, the pins block the movement. The entire operation is purely mechanical: the key overcomes spring tension or gravity to extend or retract the bolt(s) (Master Locksmiths Association, 2026).
BS 3621 is the minimum security standard for a front-door mortice deadlock in the UK
BS 3621 sets requirements for a thief-resistant mortice lock, including a minimum 20mm bolt throw, hardened steel inserts, and resistance to drilling and sawing. Locks that meet BS 3621 carry the BSI Kitemark and are often required by home insurance policies for timber front doors. Multi-point locks are not covered by BS 3621. They are tested to PAS 24, which tests the entire doorset, or TS 007, which tests the cylinder alone. If you are replacing a lock on an existing timber door, a BS 3621-rated mortice deadlock is the standard recommendation from the Association of British Insurers (ABI, 2026).
How to verify a lock installer, MCS, FENSA, or TrustMark certification matters
For uPVC or composite doors, the installer should be TrustMark-registered, which is a UK government-endorsed quality scheme, and ideally FENSA-registered for door installation (GOV.UK, TrustMark scheme, 2026). For timber doors with mortice locks, any competent locksmith can fit a new lock, but check they are registered with the Master Locksmiths Association (MLA) or have TrustMark accreditation (MLA member directory, 2026). MCS certification covers renewable energy installations only and is not relevant to door locks. If the door is being replaced as part of a new-build or renovation project, Part Q of the Building Regulations applies to new doors, and you should ask for a certificate of compliance (Legislation.gov.uk, Building Regulations Part Q, 2026). How to choose a front door installer
Frequently Asked Questions
A front door lock works by turning a key to extend a bolt or bolts from the door into the door frame. Mortice deadlocks use a single deadbolt, while multi-point systems use a central gearbox to drive hooks or rollers at three to five points along the door edge. Both types rely on the key to retract the bolts, as confirmed by British standards from GOV.UK.
A mortice deadlock is a lock fitted inside a rectangular pocket cut into the door edge. It uses a key to extend a single deadbolt horizontally into the strike plate. According to GOV.UK, a BS 3621 rated mortice deadlock has a minimum 20mm bolt throw and hardened steel inserts for thief resistance.
A multi-point locking system secures the door at three to five points with a single key turn. It uses a Euro-profile cylinder to drive hooks, rollers, or bolts at the top, middle, and bottom of the door. The Secured by Design standard confirms that many models meet PAS 24 for enhanced security.
Installing a mortice deadlock costs between £50 and £100 for labour, plus £15 to £50 for the lock. A multi-point locking system costs £80 to £200 for installation and £40 to £150 for parts. These figures are typical for UK locksmiths, according to industry pricing.
A front door lock should meet BS 3621 for mortice deadlocks or PAS 24 for multi-point locking systems. BS 3621 requires a minimum 20mm bolt throw and hardened steel inserts, while PAS 24 tests the entire doorset for forced entry resistance. Look for the BSI Kitemark or Secured by Design certification, as advised by GOV.UK.
