Window & Door Locks: Security Upgrades

Door and window locks are the first line of physical security for any property. The UK has two distinct standards frameworks, one focused on insurer requirements for existing homes (BS 3621) and one on new-build security performance (PAS 24 and Building Regulations Part Q). Understanding both helps you make informed decisions whether you are upgrading an older property or specifying security for a new build or extension.¹

Many insurers set a minimum lock standard, and if a break-in happens through a door or window that did not meet it, a theft claim can be reduced or refused.

Door Lock Standards

BS 3621: The Insurance Gold Standard

BS 3621 is the British Standard for thief-resistant lock assemblies with key egress, meaning they lock and unlock with a key from both sides.¹ It specifies minimum requirements for bolt throw, resistance to picking, drilling and sawing, and key security (a large number of key differs to make duplication harder). Some UK home insurers make BS 3621 locks on external doors a policy condition, and a compliant lock carries the BSI Kitemark and the standard number on its faceplate.²

A key distinction: BS 3621 is not limited to mortice deadlocks, the type that lock when you turn the key and do not spring shut. Approved Document Q, for example, allows a BS 3621 mortice lock paired with a surface-mounted rim lock that conforms to the same standard.¹ An ordinary nightlatch (Yale-style) that springs shut and opens from inside with a knob does not meet BS 3621, though BS 3621 rim locks with a key-locking deadlock function are available. Locks that open from inside without a key are covered instead by BS 8621 (keyless egress) and BS 10621 (dual mode).¹

PAS 24:2022: Enhanced Security Performance

PAS 24 (Publicly Available Specification) is a higher-performance standard covering the complete door set, lock, hinges, frame, and glazing, rather than just the lock cylinder. It specifies resistance to manual attack, tool attack, and cylinder manipulation. Door sets tested to PAS 24 are required for new dwellings under Building Regulations Part Q (see below).¹

The current revision is PAS 24:2022+A1:2024, amended in 2024 to keep up with changing criminal methods.³ Approved Document Q, published in 2015, still refers to PAS 24:2012.¹

Building Regulations Part Q

Part Q of the Building Regulations (England) requires that reasonable provision be made to resist unauthorised access to any new dwelling.¹ In practice this means:

• Easily accessible windows and doorsets must meet PAS 24 or equivalent, and the approved document defines that term rather than leaving it to judgement: any part within 2 m vertically of an accessible level surface such as the ground, a basement level or an access balcony, or within 2 m vertically of a flat or shallow roof, pitched under 30°, that is itself within 3.5 m of ground level. A first floor window is therefore usually outside it unless a roof or balcony brings it within reach¹
• Doorsets must be of a design shown by test to meet PAS 24 or an equivalent standard, or, for timber doors, be built to the bespoke specification in Appendix B of the approved document; easily accessible windows must also be of a design tested to PAS 24¹
• Part Q applies to new dwellings only, which includes a dwelling formed by a material change of use such as a barn or office conversion, or a house split into flats¹

Part Q does not apply to replacements in an existing dwelling, or to an extension to one (where Building Regulations generally do not require security upgrades), but PAS 24 compliance is increasingly expected by insurers on new or recently replaced door and window installations.¹

Types of Door Lock

Mortice deadlock, fitted into a slot cut in the door edge. A BS 3621 five-lever mortice deadlock is the standard insurer requirement. Key-operated from both sides; the bolt does not move without the key. Suitable for solid timber doors thick enough to take the lock case; Approved Document Q’s specification for a bespoke secure timber door calls for stiles at least 44 mm thick.¹

Multipoint lock, used on uPVC and composite doors. A central handle engages multiple locking points (hooks, rollers, deadbolts) simultaneously along the door edge when the handle is lifted and the key is turned. Multipoint locks spread the locking along the door edge, and Approved Document Q’s specification for a bespoke secure timber front door calls for a multipoint locking system to PAS 3621, PAS 8621 or PAS 10621.¹

Nightlatch (cylinder rim lock), the familiar Yale-style spring latch. Alone it is not adequate as the primary lock; it must be supplemented by a deadlock. Combined BS 3621 versions (with deadlocking function) are available.

Euro cylinder, the removable barrel used in multipoint locks and some mortice locks. Standard euro cylinders are vulnerable to snapping attacks. Anti-snap cylinders, rated TS 007 3-star or Sold Secure SS312 Diamond, are strongly recommended for any door using a euro cylinder.⁴ This is one of the most cost-effective security upgrades available.

Types of Window Lock

Cockspur handle lock, the traditional handle latch on older aluminium and uPVC casement windows. Lockable cockspur handles add a key lock to the standard handle, preventing the window being opened from outside. Very low cost; suitable for basic security in low-risk locations.

Casement espagnolette, modern uPVC casement windows use espagnolette (multi-point) locking mechanisms operated by a handle. When the handle is turned to the locked position and the key turned, multiple hooks engage the frame. This is the usual arrangement on modern uPVC casements, and for new homes Approved Document Q asks for easily accessible windows of a design shown by test to meet PAS 24.¹

Sash window locks, vertical sliding sash windows have specific lock types: fitch catches (surface-mounted, key-operated), sash stops (prevent the window opening more than a ventilation gap), and sash bolts (mortice bolts fitted to the meeting rail). A combination of a key-operated fitch catch plus sash stops on each sash is recommended.

Tilt-and-turn window locks, tilt-and-turn windows have multi-point hardware integrated into the frame that locks when the handle points down. On the usual layout, turning the handle to horizontal lets the window swing inwards on its side hinges, and turning it upright tilts it inwards from the top for ventilation; a lockable handle stops it being turned without the key.

Sold Secure Ratings

Sold Secure is a UK testing and certification house for security products, and grades them on up to four levels, though not every product category uses all four:⁵

• Bronze, resists opportunist attack with basic tools for a short period
• Silver, resists attack with more sophisticated tools for a longer period
• Gold, resists sustained, determined attack; suitable for high-risk locations
• Diamond, highest grade, reserved for the most attack-resistant products

For external door cylinders, aim for Sold Secure SS312 Diamond or TS 007 3-star. For window locks, Silver is adequate for most domestic locations.

Lock Types Comparison

Secured by Design

Secured by Design (SBD) is a police-backed accreditation scheme that certifies entire products (doors, windows, frames, hardware) rather than individual locks. For doors, the standards SBD lists are for complete doorsets, headed by PAS 24:2022+A1:2024.⁶ For new-build developers, specifying SBD-approved products is a straightforward way to demonstrate Part Q compliance, and Approved Document Q itself points to Secured by Design’s New Homes guidance for further advice.¹

For homeowners replacing windows or doors, specifying SBD-approved products provides assurance that the whole unit, frame, glazing, hardware, has been tested together, not just the lock in isolation.

Practical Advice

The cylinder is often the weakest point. On any uPVC or composite door, replace the standard euro cylinder with an anti-snap TS 007 3-star cylinder. At £20–£60 to buy, or roughly £60–£120 fitted by a locksmith, it is the single best-value security upgrade available for most UK homes.

Timber doors in Victorian and Edwardian properties may have original rim latches and no deadlock. Adding a BS 3621 mortice deadlock (assuming the door is thick enough and the stile wide enough for the lock case, measure before ordering) costs £80–£150 fitted and satisfies most insurer requirements.

Tell your insurer. If you upgrade your locks to meet BS 3621 or PAS 24, let your insurer know: some insurers make BS 3621 locks a policy condition, and meeting it can matter if you ever claim for a break-in.²

French doors and patio doors are a common weak point. Choose a doorset tested to PAS 24, with multi-point locking. Where broken glazing would let someone reach in and release the lock, Approved Document Q’s specification for bespoke timber doors calls for glass of at least class P1A to BS EN 356.¹ Surface bolts at top and bottom provide additional resistance to forced entry.

Costs given are typical UK 2026 figures including VAT. Locksmith call-out and fitting costs vary by region; London and South East rates are typically 20–30% higher than the national figures shown.