BS3621 locks explained (and what insurers mean by them)

What a BS3621 lock is, why home insurers ask for one, and the equivalent standards for uPVC and composite doors.

By LockedPrice · Updated 1 October 2026

What BS3621 is

BS3621 is the British Standard for thief-resistant locks that need a key to lock and unlock from both sides. On timber front doors it usually means a 5-lever mortice deadlock or sashlock made to the standard. Look for "BS3621" and the Kitemark stamped on the faceplate on the edge of the door.

Why insurers ask for it

Many home insurance policies require final exit doors to have a lock to BS3621 or an equivalent. If you're burgled through a door without one, a claim could be reduced or refused, so check your policy wording.

What about uPVC and composite doors?

These usually have a multipoint lock with a euro cylinder, which BS3621 doesn't cover. Insurers usually accept a multipoint lock with an anti-snap cylinder rated TS007 3 star or Sold Secure Diamond instead. Check what your policy says.

Related standards

BS8621: like BS3621 but opens from inside without a key, which is safer in a fire. Often used in flats.
PAS 24: a test standard for a whole door set rather than just the lock. Common on new-build doors.

Questions

What is a BS3621 lock?

A lock made to the British Standard for thief-resistant locks, usually a 5-lever mortice deadlock on a timber door, marked BS3621 with a Kitemark on the faceplate.

Do I need a BS3621 lock for my insurance?

Many policies require one, or an equivalent, on final exit doors. Check your policy wording.

Does BS3621 apply to uPVC doors?

Not usually. Insurers generally accept a multipoint lock with a TS007 3 star or Sold Secure Diamond cylinder instead.