What BS 3621 means for your home insurance

What BS 3621 is

BS 3621 is a British Standard published by BSI for thief-resistant locks. It covers locks that are locked and unlocked with a key from both sides of the door: mortice deadlocks, mortice sashlocks and some deadlocking rim nightlatches.

To meet the standard, a lock is tested against attack. The tests cover drilling, picking, sawing and forcing the bolt. The standard also sets a minimum number of key differs, so few other keys will open your lock, and a minimum length that the bolt must throw into the frame.

Two related standards cover locks with different ways of opening from inside:

• BS 8621 covers locks that open from inside without a key, usually with a thumb turn. They let people get out quickly in a fire.
• BS 10621 covers locks that can be switched between the two: keyless from inside while you are at home, key-only when you leave.

Why insurers ask for it

Insurers use the standard as a simple test of whether a door is reasonably secure. Many policies say that final exit doors must be fitted with a BS 3621 lock, or a lock of an equal standard. A final exit door is a door you leave by and lock from the outside.

Read your policy, not a summary. Some policies list lock requirements as a condition of cover, and not meeting them can affect a claim for theft. Others ask for them only above a certain level of cover, or not at all. If the wording is unclear, ask your insurer and keep the reply.

How to check your own lock

Open the door and look at the forend: the metal plate on the edge of the door, where the bolt comes out.

• Look for the BSI Kitemark, a small kite-shaped symbol, and the text "BS 3621". Both should be stamped into the metal.
• "5 lever" on its own is not enough. Many five-lever locks are not made to the standard.
• A lock with a latch and handles (a sashlock) can meet the standard, as long as it carries the marks.
• If the forend is painted over, or the marks are worn away, a locksmith can usually identify the lock from its make and shape.

Check every door you leave by, not only the front door.

uPVC and composite doors

Most uPVC and composite doors use a multipoint lock: hooks, rollers or bolts along the door edge, driven by a gearbox and locked with a euro cylinder. BS 3621 was not written for these locks.

For these doors, two things matter most:

• The cylinder. Euro cylinders can be attacked by lock snapping. Look for a cylinder rated TS 007 three-star, or SS312 Diamond, or a one-star cylinder fitted with two-star security handles.
• The doorset. Doors tested as a complete unit to PAS 24 have been tested against attack, including the lock, the frame and the glazing.

Insurers vary in what they accept for multipoint doors. Ask yours, and keep the cylinder's packaging or receipt as proof of its rating.

Flats and tenement doors

For a flat, the front door of the flat is usually the final exit door, not the street door of the stair. Older Edinburgh flat doors often have two locks: a mortice deadlock in the edge of the door and a rim nightlatch on the inside face.

A nightlatch that only latches is not a BS 3621 lock. Some deadlocking nightlatches are made to the standard and carry the marks. If your policy asks for one BS 3621 lock, the mortice deadlock is usually the one to check.

What to do if your lock does not meet it

A new BS 3621 mortice lock can often be fitted into the same cut-out as the old lock, if it is the same size. If not, the door is adapted to take it.

Keep the receipt or invoice, which should name the lock and the standard. If your insurer ever asks, you can show what was fitted and when.

If you rent your home, speak to your landlord before changing a lock.