British Standard Locks Explained: The Complete BS3621 Guide

If you own a home in Bishop’s Stortford, you’ve probably heard the term “British Standard locks” mentioned in insurance documents or by locksmiths.

But what does BS3621 actually mean?
And do you need one?

This guide explains everything homeowners need to know about BS3621 locks, insurance requirements, and how to check if your doors are compliant.

What Is a British Standard Lock (BS3621)?

BS3621 refers to a security standard set by the British Standards Institution (BSI) for thief-resistant locks fitted to external doors.

To achieve BS3621 certification, a lock must pass strict tests for:

• Resistance to picking

• Drilling resistance

• Forced entry

• Bolt strength

• Attack durability

Locks that meet this standard are officially stamped with the BSI Kitemark.

Why Does BS3621 Matter?

The main reason BS3621 matters is insurance compliance.

Most UK home insurance policies require:

• A 5-lever mortice deadlock conforming to BS3621

• On all final exit doors (usually front and back doors)

If your locks do not meet this standard and a burglary occurs, your insurer may question your claim.

For homeowners in Bishop’s Stortford, ensuring compliance protects both your property and your policy.

What Does a BS3621 Lock Look Like?

The most common BS3621 lock is a:

🔐 5-Lever Mortice Deadlock

Typically fitted to:

• Wooden front doors

• Traditional timber back doors

You can identify one by:

✔ A BSI Kitemark stamped on the faceplate
✔ “BS3621” engraved on the lock
✔ A substantial bolt that extends deep into the frame

If you cannot see these markings, the lock may not be certified.

BS3621 vs Standard Mortice Locks

Not all 5-lever locks meet British Standard.

Here’s the difference:

The additional security features make a significant difference in resisting forced entry.

What About uPVC and Composite Doors?

BS3621 mainly applies to wooden doors.

If your home in Bishop’s Stortford has uPVC or composite doors, you likely have a:

• Multipoint locking system

• Euro cylinder lock

In this case, insurers may require:

• TS007 3-Star rated cylinders

• Or Sold Secure approved locks

Anti-snap euro cylinders are strongly recommended for modern doors.

Do All External Doors Need BS3621 Locks?

Typically:

• Front door – Yes

• Back door – Yes

• Internal doors – No

• Patio doors – Must meet equivalent security standards

Always check your specific insurance policy wording for exact requirements.

How to Check If Your Locks Meet BS3621

Follow this quick checklist:

🔍 Step 1: Look at the Edge of the Door

Open the door and inspect the metal faceplate on the edge.

You should see:

• The BSI Kitemark

• “BS3621” marking

🔍 Step 2: Check the Key

BS3621 mortice locks usually have larger, more substantial keys compared to standard internal locks.

🔍 Step 3: Consider the Age

If your locks were installed before 2005–2010 and never upgraded, they may not meet modern insurance standards.

If unsure, a professional locksmith inspection is the safest option.

When Should You Upgrade to BS3621 Locks?

You should upgrade if:

• You’ve moved into a new property

• Your locks are outdated

• Your insurer requires compliance

• There has been a break-in attempt

• You want stronger security

Upgrading is a relatively small investment compared to the cost of a burglary.

Benefits of Installing BS3621 Locks

✔ Insurance compliance
✔ Stronger resistance to forced entry
✔ Improved property security
✔ Peace of mind
✔ Professional installation compatibility

For homeowners in Bishop’s Stortford and wider Hertfordshire, compliant locks are now considered standard best practice.

Are British Standard Locks Enough on Their Own?

BS3621 locks are essential — but security works best in layers.

For maximum protection, combine them with:

• Reinforced door frames

• Anti-snap cylinders (if applicable)

• Motion-sensor lighting

• Window locks

• Alarm or CCTV systems

A lock is only one part of your overall home security strategy.

How Much Does It Cost to Install a BS3621 Lock?

Costs vary depending on:

• Door type

• Number of locks required

• Labour and fitting

However, installation is typically affordable and completed quickly by a qualified locksmith.

Professional fitting ensures:

• Correct alignment

• Proper operation

• No door damage

• Full insurance compliance

Final Thoughts: Do You Need a BS3621 Lock?

If you have a wooden external door in Bishop’s Stortford, the answer is almost certainly yes.

BS3621 locks are:

• Insurance-friendly

• Security-tested

• Recognised nationwide

• A strong deterrent against forced entry

If you’re unsure whether your current locks meet the required standard, a quick professional inspection can give you clarity and confidence.

Security starts with the right hardware — and British Standard locks remain one of the most important foundations of home protection in the UK.