Mortice Locks & Yale Nightlatches

The combination of a Yale-type nightlatch and a 5-lever mortice deadlock is so common on London front doors that most insurers treat it as the baseline expectation. The nightlatch handles the everyday convenience — the door pulls shut and self-latches when you leave — while the mortice deadlock provides the structural security. The mortice sits inside a precisely cut pocket (the mortice) in the door stile, with a bolt that shoots into a reinforced striking plate in the frame. Because the bolt is fully enclosed by timber or composite on both sides when locked, it resists levering attacks far more effectively than a surface-mounted lock. Together, the two locks create the layered protection that most standard home-insurance policies refer to when they specify 'adequate door security'.

A Yale-type nightlatch — the familiar oval cylinder with the small oval turn on the inside — operates on a spring latch that retracts when you press the lever handle. The weak point of a basic nightlatch is that the latch can be pushed back with a credit card or a strip of plastic if the door fits loosely. A deadlocking nightlatch, also called an anti-pick or dead-latch model, adds a small plunger beside the main latch that freezes the latch bolt once the door closes, eliminating that vulnerability. When we fit or replace a nightlatch, we always advise on whether a deadlocking version is appropriate for your door type and rebate depth.

BS3621 is the British Standard for thief-resistant locks, and it is the specific mark that most UK home-insurance policies require when they refer to a 'British Standard' or 'insurance-approved' lock. To carry the BS3621 kite mark, a 5-lever mortice deadlock must pass tests covering pick resistance, bolt strength, key-duplication control, and the robustness of the case itself. The 5-lever mechanism means there are five levers inside the lock that must all align correctly with the key before the bolt will move — far harder to manipulate than a 2- or 3-lever lock. If your policy wording includes a clause about approved locks and your current lock does not carry the BS3621 mark, a claim following a break-in could be reduced or refused entirely. We carry BS3621-rated 5-lever mortice deadlocks as standard stock and can fit one the same day you call.

Fitting a mortice deadlock correctly is not simply a matter of drilling a hole. The mortice pocket must be cut to the exact depth and width of the lock case — usually around 76 mm for a standard British door — and the striking plate and box striker must be morticed into the frame to the same precision. A poorly cut mortice or a surface-fixed striking plate introduces weakness at the very point the standard is designed to reinforce. Our technicians measure the door thickness, check the stile width (narrow-stile doors need a slim-case variant), and confirm the backset before any cutting begins. If your door has previously had a different lock fitted, we also check that the existing pocket can be adapted cleanly rather than leaving voids that would weaken the stile.

Replacing a Yale nightlatch sounds straightforward, but several variables affect how the job is approached. First, the backset — the distance from the front face of the door to the centre of the cylinder hole — must match the new lock. Standard backsets are 40 mm or 44 mm; some older Tooting terraced doors with heavy original timber have unusual measurements that require a specific case. Second, the cylinder diameter must suit the hole already bored. Third, if the door is fitted with a letter-plate at mid-rail height, we check that the new lock case sits clear of it. We replace like-for-like where the existing position and hole size work well, but if there are signs of previous forced entry — a bowed frame, a chipped keep, or a loose cylinder — we address the frame or keep at the same time rather than fitting a new lock into a damaged mount.

For tenants in Tooting, a nightlatch replacement also raises the question of landlord or managing agent consent. If you are locked out and need urgent entry, we can open the door by the least destructive method available and explain exactly what was done. If a full lock change is needed after that, we will advise on the correct process, including giving the landlord copies of the new keys as the tenancy agreement typically requires. We work with letting agents and housing associations across the borough regularly and understand the documentation that is sometimes needed.

Every job on our list below is carried out at your property — there is no workshop visit required and no parts to source yourself. We work across Tooting, Tooting Bec, Tooting Broadway, Colliers Wood, and the surrounding SW17 and SW16 postcode districts. When you call 020 3675 7793, we confirm an exact up-front price that reflects the type of lock involved, the parts required, the time of day, and where in the area you are — then we send a technician straight away. We are usually with you in about 30 minutes, though we never guarantee a specific arrival time because London traffic is unpredictable. Our technicians carry insurance and are trained to work on timber, uPVC, and composite doors without causing unnecessary damage to the door leaf or frame.

Here is a specific list of the lock fitting and replacement services we carry out: fitting a new BS3621 5-lever mortice deadlock to a timber front door; replacing a worn or seized 5-lever mortice deadlock; upgrading a 2- or 3-lever mortice lock to a full BS3621 5-lever model; cutting a new mortice pocket for a first-time deadlock installation; fitting a deadlocking Yale-type nightlatch; replacing a standard nightlatch with a deadlocking anti-pick model; fitting a nightlatch to a door that has only a mortice lock currently; replacing a loose or damaged nightlatch cylinder; adjusting a nightlatch strike keep that is misaligned and causing the latch to stick; reinforcing a striking plate with a long-reach box striker for extra resistance; fitting a sashlock (combined latch and deadlock in a single mortice case) to a back door or gate-access door; replacing a sashlock after a failed break-in attempt; aligning and adjusting a mortice deadlock bolt that no longer shoots cleanly; repairing or replacing a damaged mortice case without altering the door; fitting a rim lock (rim deadlock) to a secondary or communal entrance door; replacing a faulty rim lock cylinder; adjusting or replacing a nightlatch lever handle that has become stiff or dropped; fitting British Standard night-latch cylinders to doors where only the cylinder needs updating; upgrading a standard nightlatch cylinder to a high-security anti-pick, anti-drill cylinder; assessing a door for the correct lock combination following a move-in; advising on and fitting supplementary security measures such as door-chain fittings or hinge bolts alongside a primary lock change; attending a Tooting property after a break-in to make the door secure before formal repairs; fitting temporary security while a damaged door awaits a replacement frame; attending for a door lock replacement London-wide where our coverage extends to neighbouring boroughs on request; and providing an assessment of whether a uPVC or composite door's existing euro cylinder is at snapping risk and advising on TS007-rated alternatives where relevant — though that specific uPVC cylinder service is detailed separately on our uPVC door lock repair page.

We do not quote a flat rate for mortice or nightlatch work, because the right price for a job depends on several genuine variables: the type and specification of lock required, whether parts need to be sourced from the van stock or ordered, the complexity of the door — including whether the frame needs attention — the time of day, and your location within the area. Work carried out late in the evening, overnight, or on bank holidays reflects the cost of providing round-the-clock cover. None of this is hidden — we tell you the exact figure on the phone before anyone travels to you, and that figure does not change once we arrive unless the scope of work turns out to be genuinely different from what was described. If the door is more damaged than it looked, or if a second issue is discovered once a lock is opened, we explain the situation and confirm any revised figure before proceeding. You are never committed to a cost you have not agreed.